LTC1760CFW#PBF_技术文档

LTC1760

Dual Smart Battery

System Manager

FEATURES

DESCRIPTION

The LTC^®1760 Smart Battery System Manager is a highly-

integrated SMBus Level 3 battery charger and selector

intended for products using dual smart batteries. Three

SMBus interfaces allow the LTC1760 to servo to the

internal voltage and currents measured by the batteries

while allowing an SMBus Host device to monitor either

battery’s status. Charging accuracy is determined by the

battery’s internal voltage and current measurements,

typically better than 0.ꢀ2.

n

SMBus Charger/Selector for Two Smart Batteries*

n

Voltage and Current Accuracy within 0.2% of Value

Reported by Battery

n

Simplifies Construction of “Smart Battery System

Manager”

n

Includes All SMBus Charger V1.1 Safety Features

n

Supports Autonomous Operation without a Host

n

Allows Both Batteries to Discharge Simultaneously

into Single Load with Low Loss (Ideal Diode)

n

A proprietary PowerPatharchitecture supports simultane-

ouschargingordischargingofbothbatteries.Typicalbattery

run times are extended by up to 102, while charging times

are reduced by up to 502. The LTC1760 automatically

switchesbetweenpowersourcesinlessthan10µstoprevent

power interruption upon battery or wall adapter removal.

SMBus Switching for Dual Batteries with Alarm

Monitoring for Charging Battery at All Times

n

Pin Programmable Limits for Maximum Charge

Current and Voltage Improve Safety

n

Fast Autonomous PowerPath™ Switching (<10µs)

n

Low Loss Simultaneous Charging of Two Batteries

n

The LTC1760 implements all elements of a version 1.1

“SmartBatterySystemManager”exceptforthegeneration

of composite battery information. An internal multiplexer

cleanly switches the SMBus Host to either of the two

attached Smart Batteries without generating partial mes-

sages to batteries or SMBus Host. Thermistors on both

batteriesareautomaticallymonitoredfortemperatureand

disconnection information (SafetySignal).

>952 Efficient Synchronous Buck Charger

n

AC Adapter Current Limiting* Maximizes Charge Rate

n

SMBus Accelerator Improves SMBus Timing**

n

Available in 48-Lead TSSOP Package

APPLICATIONS

n

Portable Computers and Instruments

n

Standalone Dual Smart Battery Chargers

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

PowerPath is a trademark of Analog Devices, Inc. All other trademarks are the property of their

respective owners. Protected by U.S. Patents including *57ꢀ3970 **6650174.

n

Battery Backup Systems

TYPICAL APPLICATION

Dual Battery Charger/Selector System Architecture

Dual vs Sequential Charging

3500

DC

IN

BAT2

BAT1

CURRENT

3000

2500

2000

1500

1000

500

CURRENT

SEQUENTIAL

SYSTEM

POWER

0

3500

3000

2500

2000

1500

1000

500

LTC1760

BAT1

CURRENT

SMBus (HOST)

BAT2

DUAL

CURRENT

100

MINUTES

SafetySignal 1

SMBus 1

0

100

150

200 250

300

50

TIME (MINUTES)

BATTERY TYPE: 10.8V Li-Ion (MOLTECH NI2020)

REQUESTED CURRENT = 3A

SafetySignal 2

REQUESTED VOLTAGE = 12.3V

MAX CHARGER CURRENT = 4.1A

1760 TA03

SMBus 2

1760 TA01

1760fc

1

For more information www.linear.com/LTC1760

LTC1760

ABSOLUTE MAXIMUM RATINGS

PIN CONFIGURATION

(Note 1)

TOP VIEW

DCIN, SCP, SCN, CLP,

PLUS

SCH1, SCHꢀ to GND................................... –0.3V to ꢀ8V

BOOST to GND...........................................–0.3V to 37V

CSP, CSN, BAT1, BATꢀ to GND................... –0.3V to ꢀ8V

LOPWR, DCDIV to GND ............................. –0.3V to 10V

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

48 SCH2

47 GCH2

46 GCH1

45 SCH1

44 TGATE

43 BOOST

42 SW

V

PLUS

V

, SW to GND ..................................... –0.3V to 3ꢀV

BAT2

BAT1

SCN

SCP

GDCO

GDCI

GB1O

GB1I

GB2O

GB2I

41 DCIN

40 V

CC

V

, V

to GND.......................................–0.3V to 7V

CCꢀ DDS

SDA1, SDAꢀ, SDA, SCL1,

39 BGATE

38 PGND

37 COMP1

36 CLP

35 CSP

34 CSN

LOPWR

SCLꢀ, SCL, SMBALERT to GND....................–0.3V to 7V

MODE to GND .................................–0.3V to V

V

SET

I

+0.3V

TH

CCꢀ

I

SET

COMP1 to GND ............................................ –0.3V to 5V

Maximum DC Current Into Pin

SDA1, SDAꢀ, SDA, SCL1, SCLꢀ, SCL ................ 3mA

TH1A, THꢀA..................................................... –5mA

TH1B, THꢀB ................................................... –10ꢀµA

Operating Junction Temperature Range

33 V

DCDIV

SCL2

SCL

SCL1

V

LIMIT

32 I

LIMIT

31 TH1B

30 TH1A

29 SMBALERT

28 TH2A

27 TH2B

DDS

SDA2 21

SDA 22

SDA1 23

GND 24

26 MODE

25 V

CC2

(Note 6).................................................. –40°C to 1ꢀ5°C

Storage Temperature.............................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)...................300°C

FW PACKAGE

48-LEAD PLASTIC TSSOP

T

= 1ꢀ5°C, q = 110°C/W

JA

JMAX

ORDER INFORMATION

(http://www.linear.com/product/LTC1760#orderinfo)

LEAD FREE FINISH

LTC1760CFW#PBF

LTC1760IFW#PBF

TAPE AND REEL

PART MARKING

LTC1760CFW

LTC1760IFW

PACKAGE DESCRIPTION

48-Lead Plastic TSSOP

TEMPERATURE RANGE

0°C to 85°C

LTC1760CFW#TRPBF

LTC1760IFW#TRPBF

–40°C to 1ꢀ5°C

Consult LTC Marketing for parts specified with wider operating temperature ranges.

Consult LTC Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through

designated sales channels with #TRMPBF suffix.

1760fc

2

For more information www.linear.com/LTC1760

LTC1760

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

junction temperature range, otherwise speciﬁcations are at T_A= 25°C (Note 6). V_DCIN= 20V, V_BAT1= 12V, V_BAT2= 12V, V_VDDS= 3.3V,

V_VCC2= 5.2V unless otherwise noted.

SYMBOL PARAMETER

Supply and Reference

CONDITIONS

MIN

TYP

MAX

UNITS

DCIN Operating Range

DCIN Operating Current

DCIN Selected

6

ꢀ8

V

I

Not Charging (DCIN Selected) (Note 10)

Charging (DCIN Selected) (Note 10)

1

1.3

1.5

ꢀ

mA

CH0

CH1

I

V

CCꢀ

Operating Current

AC Present (Note 11)

AC Not Present (Note 11)

0.75

75

1

100

mA

µA

VCCꢀ_AC1

VCCꢀ_AC0

Battery Operating Voltage Range

Battery Drain Current

Battery Selected, PowerPath Function

6

0

ꢀ8

V

Battery Selected, Charging Function (Note ꢀ)

I

Battery Selected, Not Charging, V

= 0V (Note 10)

175

µA

BAT

DCIN

V

Diodes Forward Voltage:

PLUS

V

DCIN to V

BAT1 to V

BATꢀ to V

I

= 10mA

= 0mA

0.8

0.7

V

FDC

FB1

FBꢀ

PLUS

VCC

SCN to V

FSCN

l

UVLO

Undervoltage Lockout Threshold

V

Ramping Down, Measured at V

to GND

3

5

5.5

1

V

PLUS

V

Regulator Output Voltage

Load Regulation

4.9

5.ꢀ

0.ꢀ

VCC

LDR

CC

V

No External Connection Beyond Applications Shown

Herein

2

Switching Regulator

l

V

Voltage Accuracy

With Respect to Voltage Reported by Battery

CHMIN

–3ꢀ

3ꢀ

mV

TOL

V

< Requested Voltage < V

LIMIT

I

Current Accuracy

With Respect to Current Reported by Battery

4mV/R < Requested Current < I (Min)

TOL

SENSE

LIMIT

(Note 1ꢀ)

l

R

ILIMIT

R

ILIMIT

R

ILIMIT

R

ILIMIT

= 0 (Short to GND)

–ꢀ

–4

–8

ꢀ

4

8

mA

= 10k 12

= 33k 12

= Open (or Short I

to V

)

LIMIT

CCꢀ

f

Regulator Switching Frequency

ꢀ55

ꢀ0

300

ꢀ5

345

kHz

0SC

Regulator Switching Frequency in Low Duty Cycle ≥992

Dropout Mode

DO

DC

Regulator Maximum Duty Cycle

99

99.5

155

150

2

mV

µA

V

MAX

I

Maximum Current Sense Threshold

CA1 Input Bias Current

V

= ꢀ.ꢀV

140

190

MAX

SNS

ITH

= V

> 5V

CSP

CSN

CMSL

CMSH

CA1 Input Common Mode Low

CA1 Input Common Mode High

CL1 Turn-On Threshold

0

V

– 0.ꢀ

V

DCIN

V

95

94

90

100

105

108

mV

CL1

l

C-Grade (Note 6)

I-Grade (Note 6)

TGATE Transition Time:

TGATE Rise Time

TGATE Fall Time

50

90

TG t

C

LOAD

C

LOAD

= 3300pF, 102 to 902

r

ns

BGATE Transition Time

BGATE Rise Time

BGATE Fall Time

50

40

90

80

ns

BG t

C

LOAD

C

LOAD

= 3300pF, 102 to 902

r

f

1760fc

3

For more information www.linear.com/LTC1760

LTC1760

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

junction temperature range, otherwise speciﬁcations are at T_A= 25°C (Note 6). V_DCIN= 20V, V_BAT1= 12V, V_BAT2= 12V, V_VDDS= 3.3V,

V_VCC2= 5.2V unless otherwise noted.

SYMBOL PARAMETER

Trip Points

CONDITIONS

MIN

TYP

MAX

UNITS

V

DCDIV/LOPWR Threshold

V

or V Falling

LOPWR

TR

DCDIV

C-Grade (Note 6)

I-Grade (Note 6)

l

1.166

1.16ꢀ

1.19

1.ꢀ15

V

DCDIV/LOPWR Hysteresis Voltage

DCDIV/LOPWR Input Bias Current

Short-Circuit Comparator Threshold

V

or V

Rising

30

ꢀ0

mV

nA

THYS

BVT

DCDIV

LOPWR

I

= 1.19V

ꢀ00

V

TSC

– V , V ≥ 5V

SCN CC

C-Grade (Note 6)

I-Grade (Note 6)

SCP

l

90

88

100

115

mV

V

Fast PowerPath Turn-Off Threshold

Overvoltage Shutdown Threshold as a

V

Rising from V

CC

6

7

7.9

V

FTO

DCDIV

Rising from 0.8V until TGATE and BGATE

SET

Percent of Programmed Charger Voltage Stop Switching

107

2

OVSD

DACs

I

Resolution

Guaranteed Monotonic

10

6

Bits

RES

DAC

Pulse Period:

Normal Mode

DAC

10

50

15

µs

ms

t

IP

ILOW

Wake-Up Mode

Charging Current Granularity

R

ILIMIT

R

ILIMIT

R

ILIMIT

R

ILIMIT

= 0 (Short I

= 10k 12

= 33k 12

to GND)

1

ꢀ

4

mA

LIMIT

= Open (or Short I

to V

)

LIMIT

CCꢀ

I

Wake-Up Charging Current (Note 5)

Charging Current Limit

60

80

100

mA

WAKE_UP

C-Grade (Note 6)

LIMIT

l

980

1000

ꢀ000

3000

4000

1070

ꢀ140

3ꢀ10

4ꢀ80

mA

R

= 0 (Short I

= 10k 12

= 33k 12

to GND)

ILIMIT

LIMIT

1960

ꢀ490

39ꢀ0

= Open (or Short I

to V

)

LIMIT

CCꢀ

I-Grade (Note 6)

R

ILIMIT

R

ILIMIT

R

ILIMIT

R

ILIMIT

= 0 (Short I

= 10k 12

= 33k 12

to GND)

l

930

1000

ꢀ000

3000

4000

1110

ꢀꢀꢀ0

33ꢀ0

4430

mA

LIMIT

1870

ꢀ380

3750

= Open (or Short I

to V

LIMIT

V

Resolution

Granularity

Guaranteed Monotonic (5V < V < ꢀ5V)

11

Bits

mV

RES

DAC

BAT

16

STEP

LIMIT

l

Charging Voltage Limit

(Note 7)

R

VLIMIT

R

VLIMIT

R

VLIMIT

R

VLIMIT

R

VLIMIT

= 0 (Short V

= 10k 12

= 33k 12

= 100k 12

to GND)

8400

1ꢀ608

1683ꢀ

ꢀ10ꢀ4

843ꢀ

1ꢀ640

16864

ꢀ1056

3ꢀ768

8464

1ꢀ67ꢀ

16896

ꢀ1088

mV

LIMIT

= Open (or Short V

to V

)(Note 13)

LIMIT

CCꢀ

Charge MUX Switches

t

GCH1/GCHꢀ Turn-On Time

GCH1/GCHꢀ Turn-Off Time

V

– V

> 3V, C = 3000pF

LOAD

5

10

ms

µs

ONC

GCHX

SCHX

V

– V

< 1V, from Time of

= 3000pF

15

OFFC

< V

– 30mV, C

CSN

BATX

LOAD

V

CH Gate Clamp Voltage

GCH1

GCHꢀ

I

= 1µA

CON

LOAD

V

– V

5

5.8

7

V

GCH1

GCHꢀ

SCH1

SCHꢀ

1760fc

4

For more information www.linear.com/LTC1760

LTC1760

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

junction temperature range, otherwise speciﬁcations are at T_A= 25°C (Note 6). V_DCIN= 20V, V_BAT1= 12V, V_BAT2= 12V, V_VDDS= 3.3V,

V_VCC2= 5.2V unless otherwise noted.

SYMBOL PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

V

CH Gate Off Voltage

GCH1

I

=10µA

COFF

TOC

FC

LOAD

V

– V

–0.8

–0.4

0

V

GCH1

GCHꢀ

SCH1

SCHꢀ

GCHꢀ

CH Switch Reverse Turn-Off Voltage

V

– V , 5V ≤ V

≤ ꢀ8V

BATX

CSN

BATX

l

C-Grade (Note 6)

I-Grade (Note 6)

5

ꢀ

ꢀ0

40

mV

l

CH Switch Forward Regulation Voltage

V

– V

, 5V ≤ V

15

35

60

mV

CSN

BATX

GCH1/GCHꢀ Active Regulation:

Max Source Current

Max Sink Current

– V

= 1.5V

SCHX

GCHX

I

–ꢀ

ꢀ

µA

OC(SRC)

OC(SNK)

V

BATX Voltage Below Which

Charging is Inhibited

(Note 14)

3.5

4.7

V

CHMIN

PowerPath Switches

t

Blanking Period after UVLO Trip

Blanking Period after LOPWR Trip

GB1O/GBꢀO/GDCO Turn-On Time

Switches Held Off

Switches in 3-Diode Mode

< –3V, from Time of Battery/DC

ꢀ50

1

ms

sec

µs

DLY

PPB

l

V

5

10

7

ONPO

GS

Removal, or LOPWR Indication, C

= 3000pF

LOAD

t

GB1O/GBꢀO/GDCO Turn-Off Time

V

> –1V, from Time of Battery/DC

3

µs

OFFPO

GS

Removal, or LOPWR Indication, C

LOAD

V

Output Gate Clamp Voltage

I

LOAD

= 1µA

PONO

POFFO

TOP

GB1O

GBꢀO

GDCO

Highest (V

or V ) – V

4.75

6.ꢀ5

7

V

BAT1

BATꢀ

DCIN

SCP

GB1O

GBꢀO

GDCO

or V ) – V

SCP

or V ) – V

SCP

Output Gate Off Voltage

I

= –ꢀ5µA

LOAD

GB1O

GBꢀO

GDCO

Highest (V

or V ) – V

0.18

0.ꢀ5

V

BAT1

BATꢀ

DCIN

SCP

GB1O

GBꢀO

GDCO

or V ) – V

SCP

or V ) – V

SCP

PowerPath Switch Reverse

Turn-Off Voltage

V

– V

SCP

or V – V

SCP DCIN

SCP

BATX

6V ≤ V

≤ ꢀ8V

l

C-Grade (Note 6)

I-Grade (Note 6)

5

ꢀ

ꢀ0

60

mV

l

PowerPath Switch Forward

Regulation Voltage

V

– V

SCP

or V

– V

SCP

0

ꢀ5

50

mV

FP

BATX

SCP

DCIN

6V ≤ V

≤ ꢀ8V

GDCI/GB1I/GBꢀI Active Regulation:

Source Current

Sink Current

(Note 3)

I

–4

75

µA

OP(SRC)

OP(SNK)

t

Gate B1I/BꢀI/DCI Turn-On Time

Gate B1I/BꢀI/DCI Turn-Off Time

V

< –3V, C

> –1V, C

= 3000pF (Note 4)

300

10

µs

ONPI

GS

LOAD

OFFPI

LOAD

V

Input Gate Clamp Voltage

I

= 1µA

LOAD

PONI

GB1I

GBꢀI

GDCI

Highest (V

or V ) – V

4.75

6.7

7.5

V

BAT1

BATꢀ

DCIN

SCP

GB1I

GBꢀI

GDCI

or V ) – V

SCP

or V ) – V

SCP

V

POFFI

Input Gate Off Voltage

I

= –ꢀ5µA

LOAD

GB1I

GBꢀI

GDCI

Highest (V

or V ) – V

0.18

0.ꢀ5

V

BAT1

BATꢀ

DCIN

SCP

GB1I

GBꢀI

GDCI

or V ) – V

SCP

or V ) – V

SCP

1760fc

5

For more information www.linear.com/LTC1760

LTC1760

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

junction temperature range, otherwise speciﬁcations are at T_A= 25°C (Note 6). V_DCIN= 20V, V_BAT1= 12V, V_BAT2= 12V, V_VDDS= 3.3V,

V_VCC2= 5.2V unless otherwise noted.

SYMBOL PARAMETER

Thermistor

CONDITIONS

MIN

TYP

MAX

UNITS

l

Thermistor Trip

C

= 300pF (Note 9)

95

100

105

kΩ

LOAD(MAX)

R1A = RꢀA = 1130Ω 12

R1B = RꢀB = 54900Ω 12

COLD-RANGE to OVER-RANGE

Thermistor Trip

IDEAL-RANGE to COLD-RANGE

C

= 300pF (Note 9)

ꢀ8.5

30

3ꢀ.5

kΩ

LOAD(MAX)

R1A = RꢀA = 1130Ω 12

R1B = RꢀB = 54900Ω 12

Thermistor Trip

HOT-RANGE to IDEAL-RANGE

C

= 300pF (Note 9)

LOAD(MAX)

R1A = RꢀA = 1130Ω 12

R1B = RꢀB = 54900Ω 12

C-Grade (Note 6)

l

ꢀ.85

ꢀ.83

3

3.15

kΩ

I-Grade (Note 6)

l

Thermistor Trip

UNDER-RANGE to HOT-RANGE

C

= 300pF (Note 9)

4ꢀ5

500

575

Ω

LOAD(MAX)

R1A = RꢀA = 1130Ω 12

R1B = RꢀB = 54900Ω 12

Logic Levels

l

SCL/SCL1/SCLꢀ/SDA/SDA1/

0.8

v

SDAꢀ Input Low Voltage (V )

IL

SCL/SCL1/SCLꢀ/SDA/SDA1/

ꢀ.1

–5

SDAꢀ Input High Voltage (V )

IH

SCL/SCL1/SCLꢀ/SDA/SDA1/

SDAꢀ Input Leakage Current

V

, V , V

SDAꢀ SCLꢀ

, V

,

5

µA

SDA SCL SDA1 SCL1

, V

= 0.8V

SCL/SCL1/SCLꢀ/SDA/SDA1/

SDAꢀ Input Leakage Current

V

, V , V

, V

,

–5

SDA SCL SDA1 SCL1 SDAꢀ

= ꢀ.1V

SCLꢀ

I

SCL1/SDA1/SCLꢀ/SDAꢀ Pull-Up

Current When Not Connected to

SMBus Host

V

, V , V , V = 0.4V

SCL1 SDA1 SCLꢀ SDAꢀ

165

ꢀꢀ0

350

PULLUP

= 4.85V and 5.55V (Current is Through

VCCꢀ

Internal Series Resistor and Schottky to V

)

CCꢀ

l

SCL1/SDA1/SCLꢀ/SDAꢀ

V

, V

= 0.8V

300

0.4

Ω

V

SDA1 SCL1 SDAꢀ SCLꢀ

Series Impedance to Host SMBus

SCL/SDA Output Low Voltage (V ).

LTC1760 Driving the Pin

I

= 350µA

OL

PULLUP

SCL1/SDA1/SCLꢀ/SDAꢀ Pullup

Internal to LTC1760

V

Output Low Voltage (V ).

OL

LTC1760 Driving the Pin with Battery

SMBus not Connected to Host SMBus

l

SCL1/SDA1/SCLꢀ/SDAꢀ

I

= 350µA on Host Side

0.4

ꢀ

V

PULLUP

Output Low Voltage (V ).

OL

LTC1760 Driving the Pin with Battery

SMBus Connected to Host SMBus

l

SCL/SCL1/SCLꢀ/SDA/SDA1/ SDAꢀ/

SMBALERT Power Down Leakage

V

= 0V, V

SCL SCL1 SCLꢀ SDA

= 0V,

VDDS

µA

VCCꢀ

, V

,

, V

= 5.5V

SDA1 SDAꢀ SMBALERT

SMBALERT Output Low Voltage (V

)

OL

I

= 500µA

PULLUP

0.4

17.5

1.5

V

SMBALERT Output Pull-Up Current

V

= 0.4V

3.5

10

µA

SMBALERT

l

V

DDS

V

DDS

V

DDS

V

DDS

Input Low Voltage (V )

V

IL_VDDS

IH_VDDS

IL

IH

ꢀ.6

3

Input High Voltage (V )

5.5

18

V

Operating Voltage

Operating Current

µA

V

, V

= V

, V

VDDS

= 5V

SCL SDA

VDDS

l

V

MODE Input Low Voltage (V )

= 4.85V

V • 0.3

VCCꢀ

V

IL_MODE

IL

VCCꢀ

1760fc

6

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LTC1760

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

junction temperature range, otherwise speciﬁcations are at T_A= 25°C (Note 6). V_DCIN= 20V, V_BAT1= 12V, V_BAT2= 12V, V_VDDS= 3.3V,

V_VCC2= 5.2V unless otherwise noted.

SYMBOL PARAMETER

MODE Input High Voltage (V )

CONDITIONS

= 4.85V

MIN

V • 0.7

VCCꢀ

TYP

MAX

UNITS

V

l

V

IH_MODE

IH

VCCꢀ

MODE Input Current (I )

MODE = V

• 0.7V, V

• 0.3V, V

= 4.85V

–1

1

µA

IH

VCCꢀ

MODE Input Current (I )

µA

IL

VCCꢀ

Charger Timing

l

t

Timeout for Wake-Up Charging and

Controlled Charging

140

175

1

ꢀ10

sec

TIMEOUT

t

Sampling Rate Used by the LTC1760 to

Update Charging Parameters

QUERY

SMBus Timing

SCL Serial-Clock High Period(t

l

)

At I

= 350µA, C

= 150pF (Note 8)

4

µs

ns

V

HIGH

PULLUP

LOAD

SCL Serial-Clock Low Period (t

)

4.7

LOW

PULLUP

LOAD

SDA/SCL Rise Time (t )

C

LOAD

C

LOAD

= 150pF, RPU = 9.31k (Note 8)

1000

300

r

SDA/SCL Fall Time (t )

f

SMBus Accelerator Trip Voltage Range

Start-Condition Setup Time (t

0.8

4.7

4

1.4ꢀ

)

µs

ns

SU:STA

Start-Condition Hold Time (t

SDA to SCL Rising-Edge

)

HD:STA

ꢀ50

Setup Time (t

)

SU:DAT

l

SDA to SCL Falling-Edge Hold Time,

Slave Clocking in Data (t

300

ꢀ5

ns

)

HD:DAT

t

The LTC1760 will Release the SMBus

and Terminate the Current Master or

Slave Command if the Command is not

Completed Before this Time

35

ms

TIMEOUT_

SMB

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

lower than the terminal voltage. Refer to “Operation Section 3.7” for more

information.

Note 8: C

is the combined capacitance on the host’s SMBus

LOAD

connection and the selected battery’s SMBus connection.

Note 2: Battery voltage must be adequate to drive gates of PowerPath

P-channel FET switches. This does not affect charging voltage of the

battery, which can be zero volts during wake-up charging.

Note 9: C is the maximum allowed combined capacitance on

THxA, THxB and the battery’s SafetySignalx connections.

LOAD_MAX

Note 10: Does not include current supplied by V to V

(I or

CCꢀ VCCꢀ_AC1

CC

Note 3: DCIN, BAT1, BATꢀ are held at 1ꢀV and GDCI, GB1I, GBꢀI are

forced to 10.5V. SCP is set at 1ꢀV to measure source current at GDCI,

GB1I and GBꢀI. SCP is set at 11.9V to measure sink current at GDCI, GB1I

and GBꢀI.

I

)

VCCꢀ_AC0

Note 11: Measured with thermistors not present, R

removed and SMBALERT = 1. See Applications Information section:

“Calculating IC Operating Current” for example on how to calculate total IC

operating current.

and R

ILIMIT

VLIMIT

Note 4: Extrapolated from testing with C = 50pF.

L

Note 5: Accuracy dependent upon external sense resistor and

compensation components.

Note 6: The LTC1760 is tested under pulsed load conditions such that T ≈

Note 12: Requested currents below 44mV/R

may not servo correctly

SENSE

due to charger offsets. The charging current for requested currents below

4mV/R will be between 4mV/R and (Requested Current – 8mA).

J

SENSE

T . The LTC1760C is guaranteed to meet specifications from 0°C to 70°C

Refer to Applications Information: “Setting Charger Output Current Limit”

for values of R

Note 13: This limit is greater than the absolute maximum for the charger.

Therefore, there is no effective limitation for the voltage when this option

is selected.

A

junction temperature. Specifications over the –40°C to 85°C operating

junction temperature range are assured by design, characterization and

correlation with statistical process controls. The LTC1760I is guaranteed

over the –40°C to 1ꢀ5°C operating junction temperature range.

.

SENSE

Note 7: Charger servos to the value reported by a Voltage() query. This is

the internal cell voltage measured by the battery electronics and may be

Note 14: Does not apply to Wake-Up Mode.

1760fc

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LTC1760

TYPICAL PERFORMANCE CHARACTERISTICS

Dual Battery Charge Time vs

Sequential Battery Charging

Charging Voltage Accuracy

Charging Current Accuracy

0

–5

10

5

3500

3000

2500

2000

1500

1000

500

BAT2

CURRENT

BAT1

CURRENT

SEQUENTIAL

0

–10

0

–5

3500

3000

2500

2000

1500

1000

500

BAT1

CURRENT

–15

–20

–25

–10

–15

–20

BAT2

DUAL

CURRENT

100

MINUTES

0

4700

7132

9564

11996 14428 16860

0

800

1600

2400

3200

4000

0

100

150

200 250

300

50

ChargingCurrent() (mA)

TIME (MINUTES)

ChargingVoltage() (mV)

1760 G01

1760 G02

BATTERY TYPE: 10.8V Li-Ion (MOLTECH NI2020)

REQUESTED CURRENT = 3A

REQUESTED VOLTAGE = 12.3V

MAX CHARGER CURRENT = 4.1A

1760 G03

Dual Battery Discharge Time vs

Sequential Battery Discharge

(Li-Ion)

Dual Battery Dischage Time vs

Sequential Battery Discharge

(NiMH)

Dual Charging Batteries with

Different Charge State

3500

3000

2500

2000

1500

1000

500

15

14

13

12

11

10

15

14

13

12

11

10

17.0

16.5

16.0

15.5

15.0

14.5

14.0

13.5

BAT2

VOLTAGE

BAT1

12.0

11.0

10.0

9.0

BAT1

VOLTAGE

DUAL

BAT2

VOLTAGE

DUAL

VOLTAGE

BAT2

VOLTAGE

BAT1

VOLTAGE

BAT2

8.0

BAT2

VOLTAGE

SEQUENTIAL

VOLTAGE

12.0

11.0

10.0

9.0

SEQUENTIAL

BAT1

CURRENT

BAT1

VOLTAGE

BAT1

BAT2

CURRENT

VOLTAGE

11

MINUTES

16

MINUTES

0

8.0

20 40 60 80 100

TIME (MINUTES)

120

140 160

0

160

0

20

60

80

100

140

0

20

60 80 100

140

180

40

120

40

120

1760 G04

TIME (MINUTES)

BAT1 INITIAL CAPACITY = 0%

BAT2 INITIAL CAPACITY = 90%

PROGRAMMED CHARGER CURRENT = 3A

PROGRAMMED CHARGER VOLTAGE = 16.8V

BATTERY TYPE: 10.8V Li-Ion (MOLTECH NI2020)

LOAD CURRENT = 3A

BATTERY TYPE: 12V NiMH (MOLTECH NJ1020)

1760 G06

1760 G05

LOAD: 33W

1760fc

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LTC1760

TYPICAL PERFORMANCE CHARACTERISTICS

Efficiency vs Charging Current

Load Dump

Load Regulation

100

90

80

70

60

50

40

30

20

10

0

14

12

10

8

12.4

12.3

12.2

12.1

12.0

11.9

11.8

11.7

11.6

BAT1

OUTPUT

V

= 20V

IN

V

= 12.29V

DAC

I

= 3000mA

LOAD CURRENT = 1A

T

= 25°C

A

6

LOAD

CONNECTED

4

V

= 20V

IN

= 12.288V

DAC

= 4000mA

DAC

LOAD

2

I

DISCONNECTED

T

= 25°C

A

0

2.5 4.0

–4 –2

0

2

4

6

8

10 12 14 16

0

0.025

0.10

0.50

0

1000

2000

3000

4000

TIME (ms)

I

(A)

CHARGE CURRENT (mA)

OUT

1760 G08

1760 G07

1760 G09

PowerPath Switching 1 and 2

SMBus Accelerator Operation

16

V

C

T

= 5V

C

I

A

= 20F

CC

LD

A

LOAD

= 200pF

15

14

13

12

11

10

9

= 0.8A

5V

= 25°C

T

= 25°C

LTC1760

R

= 15k

PULLUP

LOPWR

THRESHOLD

0V

8

7

6

–50 –40 –30

–20 –10

0

10 20 30 40 50

1µs/DIV

TIME (µs)

1760 G11

1960 G10

PIN FUNCTIONS

Input Power Related

side) of the sense resistor, R , in series with the three

SC

PowerPath switch pairs, for detecting short-circuit cur-

SCN (Pin 4): PowerPath Current Sensing Negative Input.

rent events.

This pin should be connected directly to the “bottom”

(output side) of the sense resistor, R , in series with the

GDCO (Pin 6): DCIN Output Switch Gate Drive. Together

with GDCI, this pin drives the gate of the P-channel switch

in series with the DCIN input switch.

SC

three PowerPath switch pairs, for detecting short-circuit

currentevents.AlsopowerstheLTC1760internalcircuitry

when all other sources are absent.

GDCI(Pin7):DCINInputSwitchGateDrive. Togetherwith

GDCO, this pin drives the gate of the P-channel switch

connected to the DCIN input.

SCP (Pin 5): PowerPath Current Sensing Positive Input.

This pin should be connected directly to the “top” (switch

1760fc

9

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LTC1760

PIN FUNCTIONS

GB1O (Pin 8): BAT1 Output Switch Gate Drive. Together

with GB1I, this pin drives the gate of the P-channel switch

in series with the BAT1 input switch.

CSP (Pin 35): Current Amplifier CA1 Input. This pin and

the CSN pin measure the voltage across the charge cur-

rent sense resistor, R

, to provide the instantaneous

SENSE

currentsignalsrequiredforbothpeakandaveragecurrent

GB1I (Pin 9): BAT1 Input Switch Gate Drive. Together with

GB1O, this pin drives the gate of the P-channel switch

connected to the BAT1 input.

mode operation.

COMP1 (Pin 37): The Compensation Node for the Am-

plifier CL1. A capacitor is required from this pin to GND

if input current amplifier CL1 is used. At input adapter

current limit, this node rises to 1V. By forcing COMP1 to

GND, amplifier CL1 will be defeated (no adapter current

limit). COMP1 can source 10µA.

GB2O (Pin 10): BATꢀ Output Switch Gate Drive. Together

with GBꢀI, this pin drives the gate of the P-channel switch

in series with the BATꢀ input switch.

GB2I (Pin 11): BATꢀ Input Switch Gate Drive. Together

withGBꢀO, thispindrivesthegateoftheP-channelswitch

connected to the BATꢀ input.

BGATE (Pin 39): Drives the gate of the bottom external

MOSFET of the battery charger buck converter.

CLP (Pin 36): The Positive Input to the Supply Current

LimitingAmplifierCL1.Thethresholdissetat100mVabove

the voltage at the DCIN pin. When used to limit supply

current, a filter is needed to filter out the switching noise.

SW (Pin 42): PWM Switch Node. Connected to the source

of the top external MOSFET. Used as reference for top

gate driver.

BOOST (Pin 43): Supply to Topside Floating Driver. The

bootstrap capacitor is returned to this pin. Voltage swing

at this pin is from a diode drop below V to (DCIN + V ).

Battery Charging Related

V

(Pin 13): The Tap Point of a Programmable Resistor

SET

CC

Divider which Provides Battery Voltage Feedback to the

TGATE(Pin44):DrivesthegateofthetopexternalMOSFET

of the battery charger buck converter.

Charger. A capacitor from CSN to V and from V to

SET

GND provide necessary compensation and filtering for

the voltage loop.

SCH1 (Pin 45), SCH2 (Pin 48): Charger MUX N-Channel

Switch Source Returns. These two pins are connected to

the sources of the back-to-back switch pairs Q3/Q4 and

Q9/Q10 (see Typical Applications). A small pull-down cur-

rent source returns these nodes to 0V when the switches

are turned off.

I

(Pin 14): The Control Signal of the Inner Loop of the

TH

Current Mode PWM. Higher I voltage corresponds to

TH

higher charging current in normal operation. A capacitor

of at least 0.1µF to GND filters out PWM ripple. Typical

full-scale output current is 30µA. Nominal voltage range

for this pin is 0V to ꢀ.4V.

GCH1 (Pin 46), GCH2 (Pin 47): Charger MUX N-Channel

Switch Gate Drives. These two pins drive the gates of the

back-to-back switch pairs, Q3/Q4 and Q9/Q10, between

the charger output and the two batteries (see Typical

Applications).

I

(Pin 15): A capacitor from I to GND is required to

SET

filterhigherfrequencycomponentsfromthedelta-sigmaI

.

DAC

I

(Pin 32): An external resistor (R

) is connected

ILIMIT

LIMIT

between this pin and GND. The value of the external resis-

tor programs the range and resolution of the programmed

charger current.

External Power Supply Pins

V

PLUS

(Pin 1): Supply. The V

pin is connected via

PLUS

four internal diodes to the DCIN, SCN, BAT1, and BATꢀ

pins. Bypass this pin with a 0.1µF capacitor and a 1µF

capacitor (see Typical Applications for complete circuit).

V

(Pin33):Anexternalresistor(R

)isconnected

LIMIT

VLIMIT

between this pin and GND. The value of the external resis-

tor programs the range and resolution of the voltage DAC.

BAT1 (Pin 3), BAT2 (Pin 2): These two pins are the inputs

from the two batteries for power to the LTC1760.

CSN (Pin 34): Current Amplifier CA1 Input. Connect this

to the common output of the charger MUX switches.

1760fc

10

For more information www.linear.com/LTC1760

LTC1760

PIN FUNCTIONS

LOPWR (Pin 12): LOPWR Comparator Input from SCN

ExternalResistorDividertoGND.IfthevoltageatLOPWR

pin is lower than the LOPWR comparator threshold, then

system power has failed and power is autonomously

switched to a higher voltage source, if available.

cators. RequiresanexternalpulluptoV

(normalSMBus

DDS

operating mode). Connected to internal SMBus accelerator.

SCL1(Pin19):SMBusClockSignaltoSmartBattery1. Do

not connect to an external pull-up. The LTC1760 connects

this pin to an internal pull-up (I

) when required.

PULLUP

DCDIV (Pin 16): External DC Source Comparator Input

from DCIN External Resistor Divider to GND. If the

voltage at DCDIV pin is above the DCDIV comparator

threshold, then the AC_PRESENT bit is set and the wall

adapter power is considered to be adequate to charge

SDA2 (Pin 21): SMBus Data Signal to Smart Battery ꢀ. Do

not connect to an external pull-up. The LTC1760 connects

this pin to an internal pull-up (I ) when required.

PULLUP

SDA (Pin 22): SMBus Data Signal to SMBus Host. Also

used to indicate charging status of Battery ꢀ. Requires

the batteries. If DCDIV rises more than 1.8V above V ,

CC

an external pullup to V . Connected to internal SMBus

then all of the power path switches are latched off until

all power is removed. A capacitor from DCDIV to GND is

recommendedtopreventnoise-inducedfalseemergency

turn-offconditionsfrombeingdetected.Referto“Section

8.3” and “Typical Application”.

DDS

accelerator.

SDA1 (Pin 23): SMBus Data Signal to Smart Battery 1. Do

not connect to an external pull-up. The LTC1760 connects

this pin to an internal pull-up (I ) when required.

PULLUP

DCIN(Pin41):Supply.ExternalDCpowersource.A0.1µF

bypass capacitor must be connected to this pin as close

as possible. No series resistance is allowed, since the

adapter current limit comparator input is also this pin.

MODE (Pin 26): Used in conjunction with V

to allow

DDS

SCL,SDAandSMBALERTtoindicatechargingstatus.May

also be used as a hardware charge inhibit.

TH2B (Pin 27): Thermistor Force/Sense Connection

to Smart Battery ꢀ SafetySignal. Connect to Battery ꢀ

thermistor through resistor network shown in “Typical

Application.”

Internal Power Supply Pins

V

(Pin 20): Power Supply for SMBus Accelerators.

DDS

Also used in conjunction with MODE pin to modify the

LTC1760 operating mode.

TH2A (Pin 28): Thermistor Force/Sense Connection

to Smart Battery ꢀ SafetySignal. Connect to Battery ꢀ

thermistor through resistor network shown in “Typical

Application.”

GND (Pin 24): Ground for Low Power Circuitry.

V

(Pin 25): Power Supply is used Primarily to Power

CC2

Internal Logic Circuitry. Must be connected to V .

CC

SMBALERT (Pin 29): Active Low Interrupt Pin. Signals

SMBus Host that there has been a change of status in

battery or AC presence. Open drain with weak current

PGND (Pin 38): High Current Ground Return for BGATE

Driver.

V

CC

(Pin 40): Internal Regulator Output. Bypass this

source pull-up to V

(with Schottky to allow it to be

CCꢀ

output with at least a ꢀµF to 4.7µF capacitor. Do not use

this regulator output to supply external circuitry except

as shown in the application circuit.

pulled to 5V externally). Also used to indicate charging

status of Battery 1.

TH1A (Pin 30): Thermistor Force/Sense Connection

to Smart Battery 1 SafetySignal. Connect to Battery 1

thermistor through resistor network shown in “Typical

Application.”

SBS Interface Pins

SCL2(Pin17):SMBusClockSignaltoSmartBatteryꢀ. Do

not connect to an external pull-up. The LTC1760 connects

this pin to an internal pull-up (I ) when required.

PULLUP

TH1B (Pin 31): Thermistor Force/Sense Connection

to Smart Battery 1 SafetySignal. Connect to Battery 1

thermistor through resistor network shown in “Typical

Application.”

SCL (Pin 18): SMBus Clock Signal to SMBus Host. Also

used to determine flashing rate for stand-alone charge indi-

1760fc

11

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LTC1760

BLOCK DIAGRAM

GB1I GB1O

GB2I GB2O

11 10

GDCI GDCO

9

8

7

6

100mV

SCP

SCN

5

4

+

SHORT CIRCUIT

100Ω

SWB1

DRIVER

SWB2

DRIVER

SWDC

DRIVER

–

I

32

33

LIMIT

DECODER

V

LIMIT

CHARGE

PUMP

V

CC2

DCIN

10µA

ON

–

GCH1

SCH1

46

45

+

SMBALERT

29

26

ON

–

+

SEQUENCER

MODE

GCH2

47

CSN

AC_PRESENT

V

20

18

22

19

23

17

DDS

SCH2

BAT1

48

3

SCL

SDA

SMBus

INTERFACE

2

BAT2

SCL1

SDA1

SCL2

CHARGE

V

1

SCN

PLUS

21 SDA2

V

25

40

24

CC2

V

CC

TH1A

TH1B

30

31

28

27

15

V

CC

REGULATOR

SAFETY

SIGNAL

GND

TH2A

TH2B

DECODER

+

–

16

DCDIV

I

PowerPath

CONTROLLER

10-BIT ∆Σ

CURRENT DAC

SET

+

–

LOPWR

DCIN

12

41

1.19V

CSP-CSN

3kΩ

–

0.86V

3k

0V

–

CSP

CSN

35

34

CSN

OSCILLATOR

+

–

CA1

+

LOW DROP

DETECT

BGATE

T

ON

g

= 1.4m

–

+

m

CA2

43

44

42

BOOST

TGATE

SW

0.8V

BUFFERED I

+

TH

15

S

+

PWM

LOGIC

–

I

Q

CMP

V

CC

3mV

–

R

BGATE

PGND

39

38

–

+

I

REV

40mV

Ω

DCIN

100mV

g = 0.4m

m

+

400k

CL1

–

Ω

36

CLP

V

13

11-BIT ∆Σ

VOLTAGE DAC

SET

g

m

= 1.4m

EA

+

0.8V

37

COMP1

14

1760 BD

I

TH

1760fc

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LTC1760

(For Operation Section)

TABLE OF CONTENTS

1 Overview................................................................................................................................................................................................... 14

ꢀ The SMBus Interface................................................................................................................................................................................. 14

ꢀ.1 SMBus Interface Overview................................................................................................................................................................ 14

ꢀ.3 Description of Supported SMBus Functions ..................................................................................................................................... 17

ꢀ.3.1 BatterySystemState() (0×01) .................................................................................................................................................. 17

ꢀ.3.ꢀ BatterySystemStateCont() (0×0ꢀ)........................................................................................................................................... 18

ꢀ.3.3 BatterySystemInfo() (0×04).................................................................................................................................................... 19

ꢀ.3.4 LTC() (0×3C) ........................................................................................................................................................................... ꢀ0

ꢀ.3.5 BatteryMode() (0×03) ............................................................................................................................................................ ꢀ0

ꢀ.3.6 Voltage() (0×09)...................................................................................................................................................................... ꢀ0

ꢀ.3.7 Current() (0×0A) ..................................................................................................................................................................... ꢀ1

ꢀ.3.8 ChargingCurrent() (0×14) ....................................................................................................................................................... ꢀ1

ꢀ.3.9 ChargingVoltage() (0×15) ....................................................................................................................................................... ꢀ1

ꢀ.3.10 AlarmWarning() (0×16)........................................................................................................................................................... ꢀ1

ꢀ.3.11 AlertResponse() ...................................................................................................................................................................... ꢀꢀ

ꢀ.4 SMBus Dual Port Operation.............................................................................................................................................................. ꢀꢀ

ꢀ.5 LTC1760 SMBus Controller Operation............................................................................................................................................... ꢀ3

ꢀ.6 LTC1760 SMBALERT Operation ........................................................................................................................................................ ꢀ6

3 Charging Algorithm Overview................................................................................................................................................................... ꢀ6

3.1 Wake-Up Charging Initiation............................................................................................................................................................. ꢀ6

3.ꢀ Wake-Up Charging Termination ........................................................................................................................................................ ꢀ6

3.3 Wake-Up Charging Current and Voltage Limits................................................................................................................................. ꢀ7

3.4 Controlled Charging Initiation ........................................................................................................................................................... ꢀ7

3.5 Controlled Charging Termination ...................................................................................................................................................... ꢀ7

3.6 Controlled Charging Current Programming ...................................................................................................................................... ꢀ8

3.6.1 Current Limits When Charging A Single Battery...................................................................................................................... ꢀ8

3.6.ꢀ Current Limits When Charging Two Batteries (TURBO Mode Disabled) .................................................................................. ꢀ8

3.6.3 Current Limits When Charging Two Batteries (TURBO Mode Enabled).................................................................................... ꢀ9

3.7 Controlled Charging Voltage Programming....................................................................................................................................... ꢀ9

4 System Power Management Algorithm and Battery Calibration................................................................................................................ ꢀ9

4.1 Turning Off System Power................................................................................................................................................................ ꢀ9

4.ꢀ Power-By Algorithm When No Battery is Being Calibrated................................................................................................................ ꢀ9

4.3 Power-By Algorithm When a Battery is Being Calibrated................................................................................................................... 30

4.4 Power-By Reporting.......................................................................................................................................................................... 30

5 Battery Calibration (Conditioning)............................................................................................................................................................. 30

5.1 Selecting a Battery to be Calibrated ................................................................................................................................................. 30

5.ꢀ Initiating Calibration of Selected Battery ........................................................................................................................................... 31

5.3 Terminating Calibration of Selected Battery ...................................................................................................................................... 31

6 MODE Pin Operation................................................................................................................................................................................. 31

6.1 Standalone Charge Indication ........................................................................................................................................................... 31

6.ꢀ Hardware Charge Inhibit ................................................................................................................................................................... 3ꢀ

6.3 Charging When SCL And SDA Are Low............................................................................................................................................. 3ꢀ

6.4 Charging With an SMBus Host ......................................................................................................................................................... 3ꢀ

7 Battery Charger Controller ........................................................................................................................................................................ 3ꢀ

7.1 Charge MUX Switches ...................................................................................................................................................................... 33

7.ꢀ Dual Charging ................................................................................................................................................................................... 33

8 PowerPath Controller................................................................................................................................................................................ 33

8.1 Autonomous PowerPath Switching................................................................................................................................................... 34

8.ꢀ Short-Circuit Protection.................................................................................................................................................................... 34

8.3 Emergency Turn-Off.......................................................................................................................................................................... 34

8.4 Power-Up Strategy............................................................................................................................................................................ 34

9 The Voltage DAC Block ............................................................................................................................................................................. 35

10 The Current DAC Block ............................................................................................................................................................................. 35

1760fc

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LTC1760

OPERATION (Refer to Block Diagram and Typical Application Figure)

1 Overview

diode-like behavior from the FET switches, without the

attendant high power dissipation from diodes. The Host

is informed of this 3-Diode mode status when it polls the

PowerPath status register via the SMBus interface. High

speed PowerPath switching at the LOPWR trip point is

handled autonomously.

The LTC1760 is composed of an SMBus interface with

dual port capability, a sequencer for managing system

power and the charging and discharging of two batteries,

a battery charger controller, charge MUX controller, Pow-

erPath controller, a 10-bit current DAC (I ) and 11-bit

voltage DAC (V ). When coupled with optional system

DAC

Simultaneous discharge of both batteries is supported.

The switch drivers prevent reverse current flow in the

switches and automatically discharge both batteries into

the load, sharing current according to the relative capacity

ofthebatteries.Simultaneousdualdischargecanincrease

battery operating time by up to 102 by reducing losses

in the switches and reducing internal battery losses as-

sociated with high discharge rates.

DAC

software for generating composite battery information,

it forms a complete Smart Battery System Manager for

charging and selecting two smart batteries. The battery

charger is controlled by the sequencer which uses a Level

3 SMBus interface to read ChargingVoltage(), Voltage(),

ChargingCurrent(),Current(),Alarm()andBatteryMode().

Thisinformation, together with thermistormeasurements

allows the sequencer to select the charging battery and

safely servo on voltage and current. Charging can be

accomplished only if the voltage at DCDIV indicates that

sufficientvoltageisavailablefromtheinputpowersource,

usually an AC adapter. The charge MUX, which selects

the battery to be charged, is capable of charging both

batteries simultaneously. The charge MUX switch drivers

are configured to allow charger current to share between

the two batteries and to prevent current from flowing in

a reverse direction in the switch. The amount of current

that each battery receives will depend upon the relative

capacity of each battery and the battery voltage. This can

resultinsignificantlyshorterchargingtimes(upto502for

Li-Ion batteries) than sequential charging of each battery.

2 The SMBus Interface

2.1 SMBus Interface Overview

The SMBus interface allows the LTC1760 to communi-

cate with two batteries and the SMBus Host. The SMBus

Interface supports true dual port operation by allowing

the SMBus Host to be connected to the SMBus of either

battery. The LTC1760 is able to operate as an SMBus

Master or Slave device. The LTC1760 SMBUS address is

0×14 (8-bit format).

References:

Smart Battery System Manager Specification: Revision

1.1, SBS Implementers Forum.

The sequencer also selects which of the pairs of PFET

switches will provide power to the system load. If the

system voltage drops below the threshold set by the

LOPWR resistor divider, then all of the output-side PFETs

are turned on quickly. The input-side PFETs act as diodes

in this mode and power is taken from the highest voltage

source available at the DCIN, BAT1, or BATꢀ inputs. The

input-sidePowerPathswitchdriverthatisdeliveringpower

then closes its input switch to reduce the power dissipa-

tion in the PFET bulk diode. In effect, this system provides

Smart Battery Data Specification: Revision 1.1, SBS Imp-

lementers Forum.

Smart Battery Charger Specification: Revision 1.1, SBS Imp-

lementers Forum

SystemManagementBusSpecification:Revision1.1,SBS

Implementers Forum

ꢀ

I C-Bus and How to Use it: V1.0, Philips Semiconductor.

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LTC1760

OPERATION

2.2 Data Bit Definition of Supported SMBus Functions.

LTC1760

SMBus

Mode

Data Bit or Nibble Definition/Allowed Values

(See section 2.3 for Details)

D15 D14 D13 D12 D11 D10 D09 D08 D07 D06 D05 D04 D03 D02 D01 D00

SMBus

Address

Command Data

Code

Function

Access

Type

BatterySystemState()

Slave

Read/ 7-bit:

Write 0001_010b

0×01

Status/

Control

8-bit:

0×14

0

0/1 0/1 0

0

0/1 0/1 0

0

0/1 0/1 0

0 0/1 0/1

BatterySystemStateCont()

Slave

Read/ 7-bit:

Write 0001_010b

0×0ꢀ

Status/

Control

8-bit:

0×14

0

0/1 0/1 0 0/1 0/1 0/1 0/1 1 0/1 0/1

BatterySystemInfo()

LTC()

Slave

Read 7-bit:

0001_010b

0×04

0×3C

Status

BATTERY

SYSTEM

REVISION

BATTERY

RESERVED

SUPPORTED

8-bit:

0×14

0

1

0

1

Read/ 7-bit:

Write 0001_010b

Status/

Control

8-bit:

0×14

0/1 0

0

1

0/1 0

0

1

BatteryMode()

Master

Read 7-bit:

0001_011b

0×03

Status

8-bit:

0×16

0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1

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LTC1760

OPERATION

Data Bit or Nibble Definition/Allowed Values

(See section 2.3 for Details)

LTC1760

Mode

SMBus

Address

Command Data

Function

Access

Code

Type D15 D14 D13 D12 D11 D10 D09 D08 D07 D06 D05 D04 D03 D02 D01 D00

Current()

Master

Read 7-bit:

0001_011b

0×0A

Value

8-bit:

0×16

0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1

Voltage()

Read 7-bit:

0001_011b

0×09

0×14

0×15

0×16

Status/

Control

8-bit:

0×16

0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1

Status

ChargingCurrent()

ChargingVoltage()

AlarmWarning()

Read 7-bit:

0001_011b

8-bit:

0×16

0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1

Read 7-bit:

0001_011b

Status/

Control

8-bit:

0×16

0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1

Status

Read 7-bit:

0001_010b

8-bit:

0×16

0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1 0/1

Register

AlertResponse()

see (1)

Slave

Read

Byte

7-bit:

0001_100b

N/A

8-bit:

0×18

0

1

0

1

0

(1) Read-byte format. 0×14 is returned as the interrupt address of the LTC1760.

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LTC1760

OPERATION

2.3 Description of Supported SMBus Functions

The functions are described as follows:

Function Name() (command code)

Description:

• TheLTC1760autonomouslychangestheconfiguration

of the batteries being charged (Polling only).

Purpose:

Used by the SMBus Host to determine the present state

of the LTC1760 and the attached batteries. It also may be

used to determine the state of the battery system after

the LTC1760 notifies the SMBus Host of a change via

SMBALERT.

A brief description of the function.

Purpose:

The purpose of the function, and an example where ap-

propriate.

SMBus Protocol: Read or Write Word.

Input/Output: word – Refer to “Section ꢀ.ꢀ” for bit

mapping.

SMBus Protocol: Refer to Section ꢀ.5 and to the SMBus

specification for more details.

SMB_BAT[4:1] Nibble

Input, Output or Input/Output: A description of the data

supplied to, or returned by, the function.

Theread/writeSMB_BAT[4:1]nibbleisusedbytheSMBus

Host to select with which individual battery to commu-

nicate or to determine with which individual battery it is

communicating.

Whenever the LTC1760 encounters a valid command with

invalid data, it ACKs the command, and ignores the invalid

data. For example, if an attempt is made to select Battery

1 and ꢀ to simultaneously communicate with the system

host, the LTC1760 will just ignore the request.

For example, an application that displays the remaining

capacity of all batteries would write to this nibble to in-

dividually select each battery in turn and get its capacity.

2.3.1 BatterySystemState() (0×01)

Allowed values are:

Description:

0010b: SMBus Host is communicating with Battery ꢀ.

ThisfunctionreturnsthepresentstateoftheLTC1760and

allows access to individual batteries. The information is

broken into four nibbles that report:

0001b: SMBus Host is communicating with Battery 1.

(Power On Reset Value)

To change this nibble, set only one of the lower two bits

of this nibble high. All other values will simply be ignored.

Which battery is communicating with the SMBus Host

Which batteries, if any, or AC is powering the system

Which batteries are connected to the Smart Charger

Which batteries are present.

POWER_BY_BAT[4:1] Nibble

The read only POWER_BY_BAT[4:1] nibble is used by the

SMBus Host to determine which batteries are powering

the system. All writes to this nibble will be ignored.

The LTC1760 provides a mechanism to notify the system

whenever there is a change in its state. Specifically, the

LTC1760providesthesystemwithanotificationwhenever:

Allowed values are:

0011b: System powered by both Battery ꢀ and Battery 1

simultaneously.

• A battery is added or removed (Polling or SMBALERT).

• AC power is connected or disconnected (Polling or

0010b: System powered by Battery ꢀ only.

0001b: System powered by Battery 1 only.

0000b: System powered by AC adapter only.

SMBALERT).

• TheLTC1760autonomouslychangestheconfigura-tion

of the batteries supplying power (Polling only).

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LTC1760

OPERATION

CHARGE_BAT[4:1] Nibble

power configuration. It may also be used by the system

to prohibit any battery charging.

The read only CHARGE_BAT[4:1]nibble is used by the

SMBus Host to determine which, if any, battery is being

charged. All writes to this nibble will be ignored.

SMBus Protocol: Read or Write Word.

Input/Output: word - Refer to “Section ꢀ.ꢀ” for bit

mapping

Allowed values are:

0011b: Both Battery ꢀ and Battery 1 being charged.

0010b: Only Battery ꢀ is being charged.

0001b: Only Battery 1 is being charged.

0000b: No battery being charged.

AC_PRESENT Bit

The read only AC_PRESENT bit is used to show the user

the status of AC availability to power the system. It may

be used internally by the SMBus Host in conjunction with

other information to determine when it is appropriate to

allow a battery conditioning cycle. Whenever there is a

change in the AC status, the LTC1760 asserts SMBALERT

low. In response, the system has to read this register to

determine the actual presence of AC. The LTC1760 uses

the DCDIV pin to measure the presence of AC.

An indication that multiple batteries are being charged

simultaneously does not indicate that the batteries are

being charged at the same rate or that they will complete

their charge at the same time. To actually determine

when an individual battery will be fully charged, use the

SMB_BAT[4:1] nibble to individually select the battery of

interest and read the TimeToFull() value.

Allowed values are:

1b: The LTC1760 has determined that AC is present.

PRESENT_BAT[4:1] Nibble

0b: The LTC1760 has determined that AC is not pres-

ent.

The read only PRESENT_BAT[4:1]nibble is used by the

SMBus Host to determine how many and which batteries

are present. All writes to this nibble will be ignored.

POWER_NOT_GOOD Bit

The read only POWER_NOT_GOOD bit is used to show

thatthevoltagedeliveredtothesystemloadisinadequate.

This is determined by the LOPWR comparator.

Allowed values are:

0011b: Both Battery ꢀ and Battery 1 are present.

0010b: Only Battery ꢀ is present.

0001b: Only Battery 1 is present.

0000b: No batteries are present.

ThePOWER_NOT_GOODbitwillalsobesetiftheLTC1760

has detected a short circuit condition (see “Section 8.ꢀ”)

or an emergency turn-off condition (see “Section 8.3”).

Under either of these conditions the power paths will be

shut off even if battery or DC power is available.

2.3.2 BatterySystemStateCont() (0×02)

Allowed values are:

Description:

1b: The LTC1760 has determined that the voltage

delivered to the system load is inadequate.

This function returns additional state information of the

LTC1760 and provides a mechanism to prohibit charging.

This command also removes any requirement for the

SMBus Host to communicate directly with the charger to

obtainACpresenceinformation.WhentheLTC1760isused,

access to the charger 8-bit address, 0×01ꢀ, is blocked.

0b: The LTC1760 has determined that the voltage

delivered to the system load is adequate.

CALIBRATE_REQUEST_SUPPORT Bit

The read only CALIBRATE_REQUEST_SUPPORT bit is

always set high to indicate that the LTC1760 has a mecha-

nism to determine when any of the attached batteries are

in need of a calibration cycle.

Purpose:

Used by the SMBus Host to retrieve additional state

information from the LTC1760 and the overall system

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LTC1760

OPERATION

CALIBRATE_REQUEST Bit

CALIBRATE_BAT[4:1] Nibble

The read only CALIBRATE_REQUEST bit is set whenever

the LTC1760 has determined that one or both of the con-

nected batteries need a calibration cycle.

The read/write CALIBRATE_BAT[4:1]nibble is used by the

SMBus Host to select the battery to be calibrated or to

determine which individual battery is being calibrated.

Allowed values are:

Allowed read values are:

1b: The LTC1760 has determined that one or both

batteries requires calibration.

0010b: Battery ꢀ is being calibrated. CALIBRATE must

be 1.

0b: The LTC1760 has determined that neither battery

require calibration.

0001b: Battery 1 is being calibrated. CALIBRATE must

be 1.

CHARGING_INHIBIT Bit

0000b: No batteries are being calibrated.

Allowed write values are:

The read/write CHARGING_INHIBIT bit is used by the

SMBusHosttoinhibitchargingortodetermineifcharging

is inhibited. This bit is also set if the MODE pin is used to

inhibit charging.

0010b: Select Battery ꢀ for calibration.

0001b: Select Battery 1 for calibration.

0000b: Allow LTC1760 to choose battery to be cali-

brated.

Allowed values are:

1b: The LTC1760 will not allow any battery charging

to occur.

All other values will simply be ignored. This provides a

mechanismtoupdatetheotherBatterySystemStateCont()

bits without altering this nibble.

0b: The LTC1760 may charge batteries as needed,

(Power On Reset Value).

2.3.3 BatterySystemInfo() (0×04)

CHARGER_POR Bit

Description:

The read/write CHARGER_POR bit is used to force a char-

ger power on reset.

The SMBus Host uses this function to determine the

capabilities of the LTC1760.

Writing a 1 to this bit will cause a charger power on reset

with the following effects.

Purpose:

• Charging will be turned off and wake-up charging will

be resumed. This is the same as if the batteries were

removed and then reinserted.

Allows the SMBus Host to determine the number of bat-

teries the LTC1760 supports as well as the specification

revision implemented by the LTC1760.

• The three minute wake-up watchdog timer will be

restarted.

SMBus Protocol: Read Word

Input/Output: word — Refer to “Section ꢀ.ꢀ” for bit map-

ping.

Writing a 0 to this bit has no effect. A read of this bit

always returns a 0.

BATTERIES_SUPPORTED Nibble

CALIBRATE Bit

The read only BATTERIES_SUPPORTED nibble is used

by the SMBus Host to determine how many batteries the

LTC1760 can support. The two-battery LTC1760 always

returns 0011b for this nibble.

The read/write CALIBRATE bit is used either to show the

status of battery calibration cycles in the LTC1760 or to

begin or end a calibration cycle.

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LTC1760

OPERATION

BATTERY_SYSTEM_REVISION Nibble

2.3.5 BatteryMode() (0×03)

The read only BATTERY_SYSTEM_REVISION nibble re-

ports the version of the Smart Battery System Manager

specification supported.

Description:

This function is used by the LTC1760 to read the battery’s

Mode register.

LTC1760 always returns 1000b for this nibble, indicating

Version 1.0 without optional PEC support.

Purpose:

Allows the LTC1760 to determine if a battery requires a

conditioning/calibration cycle.

2.3.4 LTC() (0×3C)

Description:

SMBus Protocol: Read Word. LTC1760 reads Battery 1

or Battery ꢀ as an SMBus Master.

This function returns the LTC version nibble and allows

the user to perform expanded Smart Battery System

Manager functions.

Input/Output: word — Refer to “Section ꢀ.ꢀ” for bit map-

ping.

Purpose:

CONDITION_FLAG Bit

Used by the SMBus Host to determine the version of

the LTC1760 and to program and monitor TURBO and

POWER_OFF special functions.

The CONDITION_FLAG bit is set whenever the battery

requires calibration.

Allowed values:

SMBus Protocol: Read or Write Word.

1b: Battery requires calibration. (Also known as a

Condition Cycle Request).

Input/Output: word — Refer to “Section ꢀ.ꢀ” for bit map-

ping.

0b: Battery does not require calibration.

POWER_OFF Bit

2.3.6 Voltage() (0×09)

This read/write bit allows the LTC1760 to turn off all

power paths.

Description:

Allowed values:

This function is used by the LTC1760 to read the actual

cell-pack voltage .

1b: All power paths are off.

0b: Allpowerpathsareenabled.(poweronresetvalue).

TURBO Bit

Purpose:

Allows the LTC1760 to determine the cell pack voltage

and close the charging voltage servo loop.

This read/write bit allows the LTC1760 to enter TURBO

charging mode. Refer to “section 3.6”.

SMBus Protocol: Read Word. LTC1760 reads Battery 1

or Battery ꢀ as an SMBus Master.

Allowed values:

Output: unsigned integer — battery terminal voltage in

milli-volts. Refer to “Section ꢀ.ꢀ” for bit mapping.

1b: Turbo charging mode enabled.

0b: Turbo charging mode disabled. (Power On Reset

Value).

Units: m V.

Range: 0 to 65,535 mV.

LTC_Version[3:0] Nibble

Thisreadonlynibblealwaysreturns0001bastheLTC1760

version.

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LTC1760

OPERATION

2.3.7 Current() (0×0A)

Description:

Purpose:

Allows the LTC1760 to determine the maximum charging

voltage.

This function is used by the LTC1760 to read the actual

current being supplied through the battery terminals.

SMBus Protocol: Read Word. LTC1760 reads Battery 1

or Battery ꢀ as an SMBus Master.

Purpose:

Output: unsigned integer — charger output voltage in mV.

Refer to “Section ꢀ.ꢀ” for bit mapping.

Allows the LTC1760 to determine how much current a

battery is receiving through its terminals and close the

charging current servo loop.

Units: m V.

SMBus Protocol: Read Word. LTC1760 reads Battery 1

Range: 0 to 65,534 mV.

or Battery ꢀ as an SMBus Master.

2.3.10 AlarmWarning() (0×16)

Output: signed integer (ꢀ’s complement) — charge/dis-

charge rate in mA increments - positive for charge, nega-

tive for discharge. Refer to “Section ꢀ.ꢀ” for bit mapping.

Description:

This function is used by the LTC1760 to read the Smart

Battery’s Alarm register.

Units: mA.

Purpose:

Range: 0 to 3ꢀ,767 mA for charge or 0 to -3ꢀ,768 mA

for discharge.

AllowstheLTC1760todeterminethestateofallapplicable

alarm flags.

2.3.8 ChargingCurrent() (0×14)

SMBus Protocol: Read Word. LTC1760 reads Battery 1

or Battery ꢀ as an SMBus Master.

Description:

This function is used by the LTC1760 to read the Smart

Battery’s desired charging current.

Output: unsigned integer – Refer to “Section ꢀ.ꢀ” for bit

mapping.

Purpose:

OVER_CHARGED_ALARM Bit

Allows the LTC1760 to determine the maximum charging

current.

The read only OVER_CHARGED_ALARM bit is used by the

LTC1760 to determine if charging may continue.

SMBus Protocol: Read Word. LTC1760 reads Battery 1

or Battery ꢀ as an SMBus Master.

Allowed values are:

1b: The LTC1760 will not charge this battery.

Output: unsigned integer — maximum charger output

current in mA. Refer to “Section ꢀ.ꢀ” for bit mapping.

0b: The LTC1760 may charge this battery if other

conditions permit charging.

Units: mA.

TERMINATE_CHARGE_ALARM Bit

Range: 0 to 65,534 mA.

The read only TERMINATE_CHARGE_ALARM bit is used

by the LTC1760 to determine if charging may continue.

2.3.9 ChargingVoltage() (0×15)

Description:

Allowed values are:

This function is used by the LTC1760 to read the Smart

Battery’s desired charging voltage.

1b: The LTC1760 will not charge this battery.

0b: The LTC1760 may charge this battery if other

conditions permit charging.

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LTC1760

OPERATION

TERMINATE_CHARGE_RESERVED Bit

2.3.11 AlertResponse()

Description:

The read only TERMINATE_CHARGE_RESERVED bit is

usedbytheLTC1760todetermineifchargingmaycontinue.

TheSMBusHostusestheAlertResponseAddress(ARA)to

simultaneously address all devices on the SMBus and de-

terminewhichdevicesarecurrentlyassertingSMBALERT.

Allowed values are:

1b: The LTC1760 will not charge this battery.

Purpose:

0b: The LTC1760 may charge this battery if other

conditions permit charging.

This command allows the SMBus Host to identify the

subset of devices that have new status data. This reduces

the number of reads required to refresh all status infor-

mation from the system. The SMBus Host begins an ARA

by transmitting the 8-bit address, 0×18, to all devices.

ARA-compliant devices that are asserting SMBALERT

will then simultaneously return their address on the next

read byte. While transmitting their address each device

monitors SDA. If a lower address is present, the device

transmitting the higher address will see that SDA does not

match and it will stop transmitting its address. When a

device sees its full address has been received it will stop

assertingSMBALERTandtheHostwillknowtoreadstatus

from this device. Subsequent ARA requests will allow the

Host to complete the list of devices requiring servicing.

OVER_TEMP_ALARM Bit

The read only OVER_TEMP_ALARM bit is used by the

LTC1760 to determine if charging may continue.

Allowed values are:

1b: The LTC1760 will not charge this battery.

0b: The LTC1760 may charge this battery if other

conditions permit charging.

TERMINATE_DISCHARGE_ALARM Bit

The read only TERMINATE_DISCHARGE_ALARM bit is

used by the LTC1760 to determine if discharge from the

battery is still allowed. This is used for PowerPath man-

agement and battery calibration.

Output:

Allowed values are:

The LTC1760 will transmit its 8-bit address, 0x14, in

response to an ARA request. The LTC1760 will stop trans-

mitting its address if another device with a lower address

is also responding to the ARA. The LTC1760 will de-assert

SMBALERT when it successfully returns its address.

1b: The LTC1760 will terminate calibration and should

try to not use this battery in the power path. When

all other power paths fail the LTC1760 will ignore

this alarm and still try to supply system power

from this battery.

The following events will cause the LTC1760 to pull-down

the SMBALERT# bus through the SMBALERT pin:

0b: TheLTC1760maycontinuedischargingthisbattery.

• Change of AC_PRESENT in the BatterySystemSta-

teCont() function.

FULLY_DISCHARGED Bit

The read only FULLY_DISCHARGED bit is used by the

LTC1760 to determine if discharge from the battery is

still allowed. This is used for PowerPath management

and battery calibration.

• Change of BATTERY_PRESENT in the BatterySys-

temState() function.

• Internal power on reset condition.

Refer to “Section ꢀ.ꢀ” for bit mapping.

Allowed values are:

1b: The LTC1760 will terminate calibration and should

try to not use this battery in the power path. When

all other power paths fail the LTC1760 will ignore

this alarm and still try to supply system power

from this battery.

2.4 SMBus Dual Port Operation

The SMBus Interface includes the LTC1760’s SMBus

controller, as well as circuitry to arbitrate and connect the

battery and SMBus Host interfaces. The SMBus controller

generates and interprets all LTC1760 SMBus functions.

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LTC1760

OPERATION

SMB2*

SMB1*

SMB2*

BAT2

BAT1

SMB*

HOST

SMB*

HOST

SMB1*

BAT1

LTC1760

SMBus

CONTROLLER

LTC1760

SMBus

CONTROLLER

HOST, LTC1760 AND BAT1 CAN COMMUNICATE.

BAT2 ORIGINATED COMMANDS ARE IGNORED.

LTC1760 AND BAT2 CAN COMMUNICATE. HOST AND

BAT1 ORIGINATED COMMANDS ARE STRETCHED IF

THE LTC1760 IS COMMUNICATING WITH BAT2.

(1a)

(1b)

SMB2*

BAT2

BAT1

BAT2

BAT1

SMB*

HOST

SMB1*

LTC1760

SMBus

CONTROLLER

LTC1760

SMBus

CONTROLLER

LTC1760 AND BAT1 CAN COMMUNICATE. HOST AND

BAT2 ORIGINATED COMMANDS ARE STRETCHED IF

THE LTC1760 IS COMMUNICATING WITH BAT1.

HOST, LTC1760 AND BAT2 CAN COMMUNICATE.

BAT1 ORIGINATED COMMANDS ARE IGNORED.

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(1c)

(1d)

*SMB INCLUDES SCL AND SDA, SMB1 INCLUDES SCL1 AND SDA1, AND SMB2 INCLUDES SCL2 AND SDA2.

Figure 1. Switch Configurations Used by the LTC1760 for Managing Dual Port Battery Communication

The dual port operation allows the SMBus Host to be

connected to the SMBus of either battery by setting the

SMB_BAT[4:1]nibble.Arbitrationishandledbystretching

anSMBusstartsequencewhenabuscollisionmightoccur.

Whenever configurations are switched, the LTC1760 will

generate a harmless SMBus reset on SMB1 and SMBꢀ as

required. The four possible configurations are illustrated

in Figure 1. Sample SMBus communications are shown

in Figures ꢀ and 3.

an invalid command code is transmitted to the LTC1760.

The SMBus Controller must respond if addressed as a

combinedSmartBatterySystemManagerat8-bitaddress

0×14. A valid address includes a legal Read/Write bit. The

SMBus Controller will ignore invalid data although the

data transmission with the invalid data will still be ACKed.

When the LTC1760, acting as a bus Master receives a

NACK, it will terminate the transmission and provide a

STOP condition on the bus.

2.5 LTC1760 SMBus Controller Operation

Detection of a STOP condition, power on reset, or SMBus

time out will reset the Controller to an initial state at any

time.

SMBuscommunicationwiththeLTC1760ishandledbythe

SMBusController,asub-blockoftheSMBusInterface.Data

is clocked into the SMBus Controller block shift register

aftertherisingSCLedge. DataisclockedoutoftheSMBus

Control block shift register after the falling edge of SCL.

The LTC1760 supports ARA, Write Word and Read Word

protocols as an SMBus Slave. The LTC1760 supports

Read Word protocol as an SMBus Master.

TheLTC1760actingasaSlavewillacknowledge(ACK)each

byte of serial data. The Command byte will be NACKed if

Refer to “System Management Bus Specification” for a

complete description of required operation and symbols.

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2.6 LTC1760 SMBALERT Operation

The LTC1760 will attempt to reinitiate wake-up charging

on a battery if the battery is not being charged, the therm-

istor is reporting IDEAL-RANGE, and the battery fails to

respond to an SMBus query. This is an important feature

for handling deeply discharged NiMH batteries. These

batteries may begin to talk while being charged and go

silent once charging has stopped.

The SMBALERT pin allows the LTC1760 to signal to the

SMBus Host that there has been a change of status.

This pin is asserted low whenever there is a change in

battery presence, AC presence or after a power on reset

event. This pin is cleared during an Alert Response or

any of the following reads:

Wake-up charging is disabled if the battery thermistor is

COLD-RANGEorUNDER-RANGEandthebatteryhasbeen

BatterySystemState(),BatterySystemStateCont(), Bat-

terySystemInfo(), or LTC().

charged for longer than t

.

TIMEOUT

3 Charging Algorithm Overview

3.1 Wake-Up Charging Initiation

3.2 Wake-Up Charging Termination

The LTC1760 will terminate wake-up charging when any

of the following conditions are met:

The following conditions must be met in order to allow

wake-up charging:

1. Battery removal (thermistor indicating OVER-RANGE)

ꢀ. AC is removed.

1. The battery thermistor must be COLD-RANGE, IDEAL-

RANGE, or UNDER-RANGE.

3. The SMBus Host issues a calibration request by setting

BatterySystemStateCont(CALIBRATE) high.

ꢀ. AC must be present.

3. BatterySystemStateCont(CHARGING_INHIBIT) must

be de-asserted (or low).

4. Any response to an LTC1760 Master read of Charging-

Current(), Current(), ChargingVoltage(), or Voltage().

Note that the LTC1760 ignores all writes from the bat-

tery.

4. Hardware controlled charging inhibit must be

de-asserted (MODE not low with V

“Section 6.ꢀ”.

high). Refer to

DDS

5. AnyofthefollowingAlarmWarning()bitsassertedhigh:

Wake-up charging initiates when a newly inserted battery

doesnotrespondtoanyLTC1760Masterreadcommands.

Only one battery will wake-up charge at a time. When two

batteries are inserted and both require wake-up charging,

Battery1willwake-upchargefirst.Batteryꢀwillonlywake-

up charge when Battery 1 terminates wake-up charging.

OVER_CHARGED_ALARM

TERMINATE_CHARGE_ALARM

TERMINATE_CHARGE_RESERVED

OVER_TEMP_ALARM

Note that the LTC1760 ignores all writes from the battery.

Eachbattery’schargealarmiscachedinsidetheLTC1760.

This internally cached bit will be set when any of the up-

per four bits of the battery’s AlarmWarning() response

are set. The cached bit will remain set if a subsequent

AlarmWarning() fails to respond. The cached alarm will

be cleared by any of the following conditions.

Wake-up charging takes priority over controlled charg-

ing; this prevents one battery from tying up the charger

when it would be advantageous to dual charge two deeply

discharged batteries.

The LTC1760 will attempt to reinitiate wake-up

charging on both batteries after the SMBus Host asserts

BatterySystemStateCont(CHARGER_POR) or a power on

reset event. This will reset any wake-up charging safety

timers and is equivalent to removing and reinserting both

batteries.

a) Associated battery is removed.

b) A subsequent AlarmWarning() clears all charge

alarm bits for the associated battery.

c) A power on reset event.

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d) The SMBus Host asserts

4. Hardware controlled charging inhibit must be

BatterySystemStateCont(CHARGER_POR) high.

de-asserted (MODE not low with V

“Section 6.ꢀ”.

high). Refer to

DDS

6. The SMBus Host asserts

BatterySystemStateCont(CHARGING_INHIBIT) high.

5. The battery responds to an LTC1760 Master read of

Alarm() with all charge alarms deasserted.

7. Hardwarecontrolledcharginginhibitisasserted(MODE

low with V

high). Refer to “Section 6.ꢀ”.

6. The battery responds to an LTC1760 Master read of

ChargingVoltage()withanonzerovoltagerequestvalue.

DDS

8. The thermistor of the battery being charged indicates

COLD-RANGE and the battery has been charged for

7. The battery responds to an LTC1760 Master read of

Voltage().

longer than t

.

TIMEOUT

9. The thermistor of the battery being charged indicates

UNDER-RANGE and the battery has been charged for

8. The battery responds to an LTC1760 Master read of

ChargingCurrent()withanonzerocurrentrequestvalue.

longer than t

.

TIMEOUT

9. The battery responds to an LTC1760 Master read of

Current().

10. The thermistor of the battery being charged indicates

HOT-RANGE.

The following charging related functions are polled each

11. Any SMBus communication line is held low for longer

t

: Alarm(), ChargingVoltage(), Voltage(), Charging-

QUERY

than t

Current(), and Current().

QUERY.

1ꢀ. BatterySystemStateCont(POWER_NOT_GOOD) is

high.

3.5 Controlled Charging Termination

The LTC1760 will terminate controlled charging when any

of the following conditions are met:

13. The emergency turn-off feature has been asserted

using the DCDIV input pin.

1. Batteryremoval,orthermistorindicatingOVER-RANGE.

ꢀ. AC removal.

3.3 Wake-Up Charging Current and Voltage Limits

The wake-up charging current is fixed at I

for all

WAKE_UP

3. The SMBus Host issues a calibration request by setting

BatterySystemStateCont(CALIBRATE) high.

values of I

. Wake-up charging uses the low current

LIMIT

mode described in “Section 10”.

4. AnLTC1760MasterreadofChargingCurrent()returning

a zero current request.

The wake-up charging voltage is not limited by the V

function.

LIMIT

5. AnLTC1760MasterreadofChargingVoltage()returning

a zero voltage request.

3.4 Controlled Charging Initiation

All of the following conditions must be met in order to

allow controlled charging of a given battery. One or both

batteries may be controlled charged at a time.

6. AnyofthefollowingAlarmWarning()bitsassertedhigh:

OVER_CHARGED_ALARM

TERMINATE_CHARGE_ALARM

TERMINATE_CHARGE_RESERVED

OVER_TEMP_ALARM

1. The battery thermistor must be COLD-RANGE, IDEAL-

RANGE, or UNDER-RANGE.

ꢀ. AC must be present.

Note that the LTC1760 ignores all writes from the battery.

Eachbattery’schargealarmiscachedinsidetheLTC1760.

This internally cached bit will be set when any of the upper

fourbitsofthebattery’sAlarmWarning()responseareset.

3. BatterySystemStateCont(CHARGING_INHIBIT) must

be de-asserted (or low).

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ThiscachedbitwillremainsetifasubsequentAlarmWarn-

ing() fails to respond. The cached alarm will be cleared by

any of the following conditions.

When charging a single battery, the charging algorithm

attempts to adjust the current so as to match the reported

current with the requested current. The LTC1760 con-

tinuously adjusts the charging current by the difference

between the actual and requested currents.

a) Associated battery is removed.

b) AsubsequentAlarmWarning()clearsallchargealarm

bits for the associated battery.

Whensimultaneouslychargingtwobatteries,thecharging

algorithm attempts to adjust the current so as to match

the reported current with the requested current in both

batteries. The LTC1760 calculates the difference between

the requested and actual current in both batteries and

uses the minimum of these differences to increment or

decrement the total charge current being provided by the

charging stage.

c) A power on reset event.

d) The SMBus Host asserts

BatterySystemStateCont(CHARGER_POR) high.

7. The SMBus Host asserts

BatterySystemStateCont(CHARGING_INHIBIT) high.

The charging algorithm will not allow the reported actual

current to exceed the requested current in either battery.

For this reason the most efficient charging occurs for

matched batteries at similar charge states.

8. Hardwarecontrolledcharginginhibitisasserted(MODE

low with V

high).

DDS

9. The SMBus of the battery being charged has stopped

acknowledgingSMBusreadcommandsforlongerthan

Whenever changing conditions cause either battery to

stop charging, the current algorithm is reset to zero. The

t

TIMEOUT.

10. The thermistor of the battery being charged indicates

HOT-RANGE.

programmed current is updated every t

.

QUERY

There are additional safety restrictions that limit the total

output current of the charger. These are detailed in the

following three sub-sections.

11. AnySMBuscommunicationlineisgroundedforlonger

than t

.

QUERY

1ꢀ. BatterySystemStateCont(POWER_NOT_GOOD) is

high.

3.6.1 Current Limits When Charging A Single

Battery

13. The emergency turn-off feature has been asserted

using the DCDIV input pin.

The following additional limits are applied to the charg-

ing current algorithm described in 3.6 when charging a

single battery:

Whenever changing conditions cause either battery to

stop charging, charging is stopped immediately for all

batteries and the voltage and current algorithms are reset

to zero. Charging is not resumed until all the conditions

for controlled charging are met.

a) The programmed current cannot exceed the re-

quested current + I

/3ꢀ.

LIMIT

b) The programmed current cannot exceed I

.

LIMIT

3.6.2 Current Limits When Charging Two Batteries

(TURBO Mode Disabled)

3.6 Controlled Charging Current Programming

TheLTC1760usesasinglechargerstagetosimultaneously

charge up to two batteries. The batteries are connected to

the charger using a charge MUX. The charge MUX allows

the total charger current to be shared by the two batteries

while preventing charge transfer between the batteries.

Refer to “Section 7.1” and “Section 7.ꢀ”.

The following additional limits are applied to the charging

current algorithm described in 3.6 when charging two

batteries with turbo mode disabled:

a) The programmed current cannot exceed the maxi-

mum of the two requested currents + I

.

LIMIT/3ꢀ

b) The programmed current cannot exceed I

.

LIMIT

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3.6.3 Current Limits When Charging Two Batteries

(TURBO Mode Enabled)

by 16mV each t

tions are met:

unless one of the following condi-

QUERY

a) The actual voltage exceeds the requested voltage in

either battery.

The following additional limits are applied to the charging

current algorithm described in 3.6 when charging two

batteries with turbo mode enabled:

b) The actual voltage exceeds V

.

LIMIT

a) The programmed current cannot exceed the maxi-

ThisisanextremelyimportantfeatureoftheLTC1760since

it allows the charger to servo on the internal cell voltage

of the battery as determined by the Smart Battery. This

voltage may be significantly lower than the battery pack

terminal voltage which is used by all Level ꢀ chargers.

The advantage for the LTC1760 is improved charge time,

safety, and a more completely charged battery.

mum of the two requested currents + I

. This

LIMIT

relaxed limit enables accelerated charging if I

is greater than the maximum of the two requested

currents. For the recommended matched battery

pair the requested current should be the same.

b) The programmed current cannot exceed I

LIMIT

TURBO mode provides a mechanism for the SMBus Host

to enable the charge MUX to apply additional current to

both batteries. TURBO mode only has an effect when two

batteries are being charged simultaneously. TURBO mode

does not affect wake-up charging or any other conditions

that could inhibit charging. TURBO mode is entered when

LTC(TURBO) is set high.

The voltage correction cannot exceed the minimum re-

questedvoltagebymorethan51ꢀmV.Whendecrementing,

the programmed voltage is reduced by 16mV each t

.

QUERY

Wheneverchangingconditionscauseeitherbatterytostop

charging, the voltage algorithm is reset to zero.

4 System Power Management Algorithm and Battery

Calibration

Normally the LTC1760 will limit the current into both bat-

teries to the maximum of the two requested currents +

4.1 Turning Off System Power

I

/3ꢀ. TURBO mode removes this restriction, allowing

LIMIT

TheLTC1760allowstheusertoturnoffsystempowerusing

the LTC(POWER_OFF) bit. When POWER_OFF is asserted

high all power management functions are bypassed and

the LTC1760 will turn off DCIN, BATꢀ and BAT1 power

paths. This feature allows the user to power down the

system. Charging is still allowed when POWER_OFF is

asserted high.

the charger to output as much as I

battery system.

into the combined

LIMIT

Forexample:InasystemwhereLTC(TURBO)=0,I

=4.0A

LIMIT

and each battery is requesting ꢀA the LTC1760 will not

outputmorethan ꢀ.1ꢀ5Aintothecombinedbatterysystem

or 1.06A into each battery if their charge states match.

In a system where LTC(TURBO)=1, I

= 4.0A and each

LIMIT

battery is requesting ꢀA the LTC1760 will now output up

4.2 Power-By Algorithm When No Battery is Being

Calibrated

to I

into the combined battery system or ꢀA into each

LIMIT

battery if their charge states match.

TheLTC1760willalwaysattempttomaintainsystempower.

The preferred configuration is to remain in 3- Diode mode.

In 3-Diode mode, power will be provided by BAT1, BATꢀ

and DCIN with the source at the highest voltage potential

automatically providing all the power. Sources at similar

voltagepotentialswillsharepowerbasedontheircapacity.

Even without TURBO mode, the LTC1760 offers signifi-

cantly reduced charge times for matched batteries in the

top-off state. This time savings is especially significant for

Lithium-Ion batteries. Simultaneously charging two bat-

teries reduces losses in switches and improves efficiency.

3.7 Controlled Charging Voltage Programming

ThefollowingconditionswillcausetheLTC1760tomodify

its preferred power-by algorithm.

The LTC1760 monitors the requested and actual voltages

in each battery and increments the programmed voltage

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1. A battery issues a TERMINATE_DISCHARGE alarm and

AC_PRESENTishigh.TheLTC1760willselecttheother

battery and DCIN to power the system.

Power Reporting with AC_PRESENT Low and both Batteries

Present, as a Function of Power Alarms.

BATTERY 2

BATTERY 1

POWER ALARM POWER ALARM POWERED_BY_

AC_PRESENT

(NOTE 1)

BAT(4:1)

ꢀ. A battery issues a TERMINATE_DISCHARGE alarm and

AC_PRESENT is low. The LTC1760 will select the other

battery to power the system.

0

1

0

1

X

0

1

0

1

X

0011b

0010b

0001b

0011b

0000b

3. A battery issues a TERMINATE_DISCHARGE alarm,

AC_PRESENTislow,andtheotherbatteryisnotpresent

or has previously issued an alarm. The LTC1760 will

autonomously try to restore power by entering 3-Diode

mode. The 3-Diode mode will ignore TERMINATE_

DISCHARGE and FULLY_DISCHARGED alarms.

Note 1: A power alarm means that ALARM() has returned

TERMINATE_DISCHARGE=1 or FULLY_DISCHARGED_ALARM=1

Power Reporting When

BatterySystemStateCont(POWER_NOT_GOOD) is High

and the LTC1760 has Autonomously Entered 3-Diode Mode

4.3 Power-By Algorithm When a Battery is Being

Calibrated

POWERED_BY_

AC_PRESENT PRESENT_BAT2 PRESENT_BAT1 BAT(4:1)

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0000b

0001b

0010b

0011b

0000b

During battery calibration, the battery being calibrated is

the only device powering the system. This will be reflected

in the reported POWER_BY[4:1] bits. See “Section 5” for

more information on battery calibration.

4.4 Power-By Reporting

The following tables illustrate how BatterySystem

State(POWER_BY_BAT[4:1]) interprets PowerPath

conditions.

5 Battery Calibration (Conditioning)

Calibration allows the SMBus Host to fully discharge

a battery for conditioning purposes. The SMBus Host

may determine the battery to be discharged or allow the

LTC1760 to choose based on the batteries’ request to

be conditioned.

Power Reporting for Batteries Being Calibrated

POWERED_BY_

AC_PRESENT CALIBRATE_BAT2 CALIBRATE_BAT1 BAT(4:1)

1

0

1

0

1

0

0000b

0001b

0010b

5.1 Selecting a Battery to be Calibrated

*States not shown are not allowed

Option 1) SMBus Host chooses battery to be calibrated

using BatterySystemStateCont(CALIBRATE_BAT[4:1])

Power Reporting as a Function of Battery Presence

POWERED_BY_

AC_PRESENT PRESENT_BAT2 PRESENT_BAT1 BAT(4:1)

Allowed values:

1

0

X

0

1

X

0

1

0

1

0000b

0001b

0010b

0011b

0001b: Set CALIBRATE_BAT1. Only has an effect if

Battery1BatteryMode(CONDITION_FLAG)ishigh.May

not be updated if a calibration is in progress.

0010b: Set CALIBRATE_BATꢀ. Only has an effect if

BatteryꢀBatteryMode(CONDITION_FLAG)ishigh.May

not be updated if a calibration is in progress.

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0000b:ClearsCALIBRATE_BAT1andCALIBRATE_BATꢀ

and allows LTC1760 to chose. Power on reset default.

May not be updated if a calibration is in progress.

• The battery sets Alarm Warning(TERMINATE_

DISCHARGE) high.

• ThebatterysetsAlarmWarning(FULLY_DISCHARGED)

high.

Option ꢀ) SMBus Host allows LTC1760 to choose battery

to be calibrated.

• A zero is written to the CALIBRATE bit.

BatterySystemStateCont(CALIBRATE_BAT[4:1]) =0000b.

See previous option.

The LTC1760 will attempt to initiate a charge cycle after

the discharge cycle is completed.

The LTC1760 determines that the battery requires

calibration by reading BatteryMode(CONDITION_FLAG).

This flag is cached in the LTC1760. The LTC1760 sets

BatterySystemStateCont(CALIBRATE_REQUEST) high.

TheLTC1760willalwaysselectthebatterythatisrequesting

calibration. If both batteries are requesting calibration, the

LTC1760 will select Battery 1. If neither battery is request-

ing calibration, then calibration cannot occur.

6 MODE Pin Operation

TheMODEpinisamultifunctionpinthatallowstheLTC1760

to: 1) display charging status in stand alone operation; ꢀ)

activate hardware charge inhibit; 3) charge when SCL and

SDA are low and; 4) charge with an SMBus Host.

Summary of SDA, SCL and SMBALERT Operation as a Function

of MODE and V_DDSLevels

CONDITION

LTC1760 OPERATING MODE

5.2 Initiating Calibration of Selected Battery

V

MODE

V

VDDS

= GND

SCL: Clock for Status Indicators

SDA: Battery ꢀ Status

The SMBus Host initiates a calibration by writing to

BatterySystemStateCont(CALIBRATE). Followrulesofthe

previous section to preserve battery intended for calibra-

tion. The SMBus Host must only set the calibration bit

once per calibration.

< V

IL_VDDS

SMBALERT: Battery 1 Status

V

MODE

V

VDDS

= GND

SCL, SDA, SMBALERT: Normal Operation

LTC1760 Charging Inhibited

> V

IH_VDDS

V

MODE

V

VDDS

= V

< V

SCL, SDA Ignored and May Float Low

SMBALERT: Normal Operation

SCL1, SDA1, SCLꢀ and SDAꢀ: Normal Operation and

Charging is Allowed

VCCꢀ

TheLTC1760willdischargetheselectedbatteryaslongas

the calibration is in progress (CALIBRATE high). Updates

to the cached BatteryMode(CONDITION_FLAG) will be

inhibited while CALIBRATE is asserted. This means that

discharge of the battery will continue even if the battery

clears the CONDITION_FLAG.

IL_VDDS

V

MODE

V

VDDS

= V

Normal Operation on all Pins, Charging is Allowed

VCCꢀ

> V

IH_VDDS

6.1 Standalone Charge Indication

When MODE is tied to GND and V

5.3 Terminating Calibration of Selected Battery

< V

, the

IL_VDDS

VDDS

Calibration will end when CALIBRATE is cleared. CALI-

BRATE will be cleared when:

function of SDA, SMBALERT, and SCL are changed as

described below:

• AC is removed.

SDA is an output and is used to monitor charging status

of Battery ꢀ. Allowed values are:

• The battery being calibrated is removed. When the

battery being calibrated is removed, the LTC1760 will

automatically calibrate the other battery if it is request-

ing calibration.

Low: Battery ꢀ is charging.

High: Battery ꢀ not charging (AC is not present or bat-

tery is not present).

• BatterySystemStateCont(POWER_NOT_GOOD)ishigh.

Blinking: Battery ꢀ charge complete (AC is present,

battery is present and not charging).

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SMBALERTisusedtomonitorchargingstatusofBattery1.

Allowed values are:

to set the bottom MOSFET on time. The result is quasi-

constant frequency operation where the converter fre-

quency remains nearly constant over a wide range of

output voltages. This activity is diagrammed in Figure 4.

Low: Battery 1 is charging.

High: Battery 1 not charging (AC is not present or bat-

tery is not present).

OFF

TGATE

ON

Blinking: Battery 1 charge complete (AC is present,

battery is present and not charging).

t

OFF

ON

BGATE

SCL is an input and is used to determine the blinking rate

of SDA and SMBALERT. Tie SCL high if blinking is not

desired. This will provide two different states to indicate

charging (output low) and not charging (output high).

OFF

TRIP POINT SET BY I VOLTAGE

TH

INDUCTOR

CURRENT

1760 F04

6.2 Hardware Charge Inhibit

Figure 4.

WhenMODEistiedtoGNDandV

>V

,charging

VDDS IH_VDDS

The peak inductor current, at which I

resets the SR

TH TH

CMP

isinhibitedandBatterySystemStateCont(CHARGING_INHIBIT)

will report a logic high.

latch, is controlled by the voltage on I . I is in turn

controlled by several loops, depending upon the situation

at hand. The average current control loop converts the

voltage between CSP and BAT to a representative current.

Error amp CAꢀ compares this current against the desired

6.3 Charging When SCL And SDA Are Low

When MODE is tied to V

and V

< V

, SDA

IL_VDDS

CCꢀ

VDDS

and SCL are not used and will not interfere with LTC1760

batterycommunication.ThisfeatureallowstheLTC1760to

autonomouslychargewhenSCLandSDAarenotavailable.

ThisscenariomightoccurwhenSMBusHosthaspowered

down and is no longer pulling up on SCL and SDA.

currentprogrammedbytheI

TH

attheI pinandadjusts

DAC

SET

I

for the desired voltage across R

.

SENSE

The voltage at BAT is divided down by an internal resis-

tor divider set by the V

and is used by error amp EA

DAC

to decrease I if the divider voltage is above the 0.8V

TH

reference.

6.4 Charging With an SMBus Host

The amplifier CL1 monitors and limits the input current,

normally from the AC adapter, to a preset level (100 mV/

When Mode is tied to V

and V

> V

, SDA

CCꢀ

VDDS

IH_VDDS

and SCL are used to communicate with the SMBus Host.

R ). At input current limit, CL1 will decrease the I volt-

CL

TH

7 Battery Charger Controller

age and thus reduce battery charging current.

The LTC1760 charger controller uses a constant off-time,

current mode step-down architecture. During normal

operation, the top MOSFET is turned on each cycle when

the oscillator sets the SR latch and turned off when the

An over-voltage comparator, OV, guards against transient

overshoots(>7.52).Inthiscase,thetopMOSFETisturned

off until the over-voltage condition is cleared. This feature

is useful for batteries which “load dump” themselves by

opening their protection switch to perform functions such

as calibration or pulse-mode charging.

main current comparator I

resets the SR latch. While

CMP

the top MOSFET is off, the bottom MOSFET is turned on

until either the inductor current trips the current compara-

The top MOSFET driver is powered from a floating boot-

strap capacitor C4. This capacitor is normally recharged

tor I , or the beginning of the next cycle. The oscillator

REV

uses the equation:

from V through an external diode when the top MOS-

CC

t

= (V

- V )/(V

• f

)

FET is turned off. As V decreases towards the selected

OFF

DCIN

BAT

DCIN OSC

IN

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battery voltage, the converter will attempt to turn on the

top MOSFET continuously (“dropout’’). A dropout timer

detects this condition and forces the top MOSFET to turn

off, and the bottom MOSFET on, for about ꢀ00ns at 40µs

intervals to recharge the bootstrap capacitor.

7.2 Dual Charging

Note that the charge MUX switch drivers will operate

together to allow both batteries to be charged simultane-

ously. If both charge MUX switch drivers are enabled,

only the battery with the lowest voltage will be charged

until its voltage rises to equal the higher voltage battery.

The charge current will then share between the batteries

according to the capacity of each battery.

7.1 Charge MUX Switches

The equivalent circuit of a charge MUX switch driver is

shown in Figure 5. If the charger controller is not enabled,

the charge MUX drivers will drive the gate and source of

the series-connected MOSFETs to a low voltage and the

switchisoff. Whenthe chargercontrolleris on, the charge

MUX driver will keep the MOSFETs off until the voltage at

CSN rises at least 35mV above the battery voltage. GCH1

is then driven with an error amplifier EAC until the volt-

age between BAT1 and CSN satisfies the error amplifier

or until GCH1 is clamped by the internal Zener diode.

The time required to close the switch could be quite long

(many ms) due to the small currents output by the error

amp and depending upon the size of the MOSFET switch.

Whenbatteriesarecontrolledcharging,onlybatterieswith

voltages above V

are allowed to charge. When a bat-

CHMIN

tery is wake-up charging this restriction does not apply.

8 PowerPath Controller

ThePowerPathswitchesareturnedonandoffbythepower

management algorithm. The external PFETs are usually

connected as an input switch and an output switch. The

output switch PFET is connected in series with the input

PFETandthepositivesideoftheshort-circuitsensingresis-

tor, R . The input switch is connected in series between

SC

the power source and the output PFET. The PowerPath

switch driver equivalent circuit is shown in Figure 6. The

output PFET is driven ON or OFF by the output side driver

controlling pin GB10. The gate of the input PFET is driven

by an error amplifier which monitors the voltage between

the input power source (BAT1 in this case) and SCP. If

the switch is turned off, the two outputs are driven to the

higher of the two voltages present across the input/SCP

terminals of the switch. When the switch is instructed to

turn on, the output side driver immediately drives the gate

of the output PFET approximately 6V below the highest

of the voltages present at the input/SCP. When the output

PFET turns on, the voltage at SCP will be pulled up to a

diode drop below the source voltage by the bulk diode of

the input PFET. If the source voltage is more than ꢀ5mV

above SCP, EAP will drive the gate of the input PFET low

until the input PFET turns on and reduces the voltage

across the input/SCP to the EAP set point, or until the

Zener clamp engages to limit the voltage applied to the

input PFET. If the source voltage drops more than ꢀ0mV

below SCP, then comparator CP turns on SWP to quickly

prevent large reverse current in the switch. This operation

mimics a diode with a low forward voltage drop.

If the voltage at CSN decreases below V

– ꢀ0mV a

BAT1

comparator CC quickly turns off the MOSFETs to prevent

reverse current from flowing in the switches. In essence,

this system performs as a low forward voltage diode.

Operation is identical for BATꢀ.

DCIN + 10V

(CHARGE PUMPED)

BAT1

CSN

TO

BATTERY

1

–

+

GCH1

SCH1

Q3

EAC

35mV

20mV

FROM

CHARGER

+

–

CC

10k

Q4

OFF

1760 F05

Figure 5. Charge MUX Switch Driver Equivalent Circuit

1760fc

33

For more information www.linear.com/LTC1760

LTC1760

OPERATION

SCN exceeds the short-circuit comparator threshold

for more than 15ms, then all of the PowerPath

20mV

OFF

–

V

TSC

CP

switches are turned off and BatterySystemState-Cont

(POWER_NOT_GOOD) is set. Similarly, if the voltage

at SCN falls below 3V for more than 15ms, then all of

the PowerPath switches are turned off and POWER_

NOT_GOOD is set high. The POWER_NOT_GOOD bit is

reset by removing all power sources and allowing the

+

FROM

BATTERY

1

BAT1

SWP

–

GB1I

Q7

Q8

EAP

SCP

+

25mV

GB1O

voltage at V

to fall below the UVLO threshold. If

PLUS

the POWER_NOT_GOOD bit is set, charging is disabled

OFF

until V

exceeds the UVLO threshold and the Charger

PLUS

Algorithm allows charging to resume.

R

SC

C

L

TO LOAD

1760 F06

When a hard short-circuit occurs, it might pull all of the

power sources down to near 0V potentials. The capacitors

Figure 6. PowerPath Driver Equivalent Circuit

on V and V

must be large enough to keep the circuit

CC

PLUS

operating correctly during the 15ms short-circuit event.

The charger will stop within a few microseconds, leaving

a small current which must be provided by the capacitor

8.1 Autonomous PowerPath Switching

The LOPWR comparator monitors the voltage at the

load through the resistor divider from pin SCN. If LTC

(POWER_OFF) is low and the LOPWR comparator trips,

then all of the switches are turned on (3-Diode mode)

by the Autonomous PowerPath Controller to ensure that

the system is powered from the source with the highest

voltage. The Autonomous PowerPath Controller waits

approximately 1 second, to allow power to stabilize, and

then reverts back to the PowerPath switch configuration

requested by the PowerPath Management Algorithm. A

power fail counter is incremented to indicate that a failure

has occurred. If the power fail counter equals a value of 3,

then the the Autonomous PowerPath Controller sets the

switches to 3-Diode mode and BatterySystem-

StateCont(POWER_NOT_GOOD) will be set, provided

the LOPWR comparator is still detecting a low power

event. This is a three-strikes-and-you’re-out process

which is intended to debounce the POWER_NOT_GOOD

indicator. The power fail counter is reset when battery or

AC presence change.

on V

. The recommended minimum values (1µF on

PLUS

V

and ꢀµF on V , including tolerances) should keep

PLUS

CC

the LTC1760 operating above the UVLO trip voltage long

enough to perform the short-circuit function when the

input voltages are greater than 8V. Increasing the capaci-

tor across V to 4.7µF will allow operation down to the

CC

recommended 6V minimum.

8.3 Emergency Turn-Off

All of the PowerPath switches can be forced off by set-

ting the DCDIV pin to a voltage between 8V and 10V. This

will have the same effect as a short-circuit event. DCDIV

must be less than 5V and V

must decrease below

PLUS

the UVLO threshold to re-enable the PowerPath switches.

The LTC1760 can recover from this condition without

removing power. Contact Applications Engineering for

more information.

8.4 Power-Up Strategy

All three PowerPath switches are turned on after V

PLUS

8.2 Short-Circuit Protection

exceeds the UVLO threshold for more than ꢀ50ms. This

delay is to prevent oscillation from a turn-on transient

near the UVLO threshold.

Short-circuit protection operates in both a current mode

and a voltage mode. If the voltage between SCP and

1760fc

34

For more information www.linear.com/LTC1760

LTC1760

OPERATION

9 The Voltage DAC Block

modulator and switch convert the I

value to a variable

DAC

resistance equal to 1.ꢀ5R /(I

/10ꢀ3). In regu-

SET DAC(VALUE)

The voltage DAC (V ) is a delta-sigma modulator

which controls the effective value of an internal resistor,

DAC

lation, I is servo driven to the 0.8V reference voltage,

SET

V

, and the current from R

is matched against a

REF

SET

R

= 7.ꢀk,usedtoprogramthemaximumchargervolt-

VSET

current derived from the voltage between pins CSP and

CSN. This current is (V – V )/3k.

age. Figure7isasimplifieddiagramoftheV

operation.

DAC

CSP

CSN

The delta-sigma modulator and switch SWV convert the

value to a variable resistance equal to (11/8)R

Therefore programmed current is:

V

/

VSET

DAC

(V

/ꢀ047). In regulation, V is servo driven to

DAC(VALUE)

SET

I

= V • 3k/(1.ꢀ5 RSNS R ) • (I

/10ꢀ3)

CHG

REF

SET

DAC(VALUE)

/10ꢀ3)

the 0.8V reference voltage, V

.

REF

= (10ꢀ.3mV/R ) • (I

SNS

DAC(VALUE)

Capacitors C and C are used to average the voltage

B1

Bꢀ

During wake-up current operation, the current DAC enters

a low current mode. The current DAC output is pulse-

width modulated with a high frequency clock having a

duty cycle value of 1/8. Therefore, the maximum output

present at the V

pin as well as provide a zero in the

SET

voltage loop to help stability and transient response time

to voltage variations.

currentprovidedbythechargerisI

/8. Thedelta-sigma

MAX

10The Current DAC Block

output gates this low duty cycle signal on and off. The

delta-sigma shift registers are then clocked at a slower

rate, about 40ms/bit, so that the charger has time to settle

ThecurrentDACisadelta-sigmamodulatorwhichcontrols

the effective value of an internal resistor, R

= 18.77k,

SET

to the I

/8 value.

usedtoprogramthemaximumchargercurrent.Figure8is

asimplifieddiagramoftheDACoperation.Thedelta-sigma

MAX

CSN

(V

CSP

– V

)

CSN

3kΩ

(FROM CA1 AMPLIFIER)

R

VF

C

B2

C

405.3k

I

SET

V

SET

+

–

+

TO

TH

TO

TH

C

SET

EA

I

B1

V

REF

V

REF

R

SET

VSET

7.2k

18.77k

DAC

VALUE

(10 BITS)

1760 F08

DAC

10

∆Σ

MODULATOR

11

∆Σ

MODULATOR

SWV

VALUE

(11 BITS)

1760 F07

Figure 7. Voltage DAC Operation

Figure 8. Current Dac Operation

1760fc

35

For more information www.linear.com/LTC1760

LTC1760

APPLICATIONS INFORMATION

Automatic Current Sharing

it is actual physical capacity rating at the time of charge.

Capacity rating will change with age and use and hence

the current sharing ratios can change over time.

In a dual parallel charge configuration, the LTC1760 does

notactuallycontrolthecurrentflowingintoeachindividual

battery. The capacity, or Amp-Hour rating, of each battery

determines how the charger current is shared. This auto-

matic steering of current is what allows both batteries to

reach their full capacity points at the same time. In other

words, given all other things equal, charge termination

will happen simultaneously.

Adapter Limiting

An important feature of the LTC1760 is the ability to auto-

matically adjust charging current to a level which avoids

overloading the wall adapter. This allows the product to

operate at the same time that batteries are being charged

without complex load management algorithms. Addition-

ally,batterieswillautomaticallybechargedatthemaximum

possible rate of which the adapter is capable.

A battery can be modeled as a huge capacitor and hence

governed by the same laws.

This feature is created by sensing total adapter output cur-

rent and adjusting charging current downward if a preset

adapter current limit is exceeded. True analog control is

used,withclosedloopfeedbackensuringthatadapterload

current remains within limits. Amplifier CL1 in Figure 9

I = C • (dV/dt) where:

I = The current flowing through the capacitor

C = Capacity rating of battery (using amp-hour values

instead of capacitance)

senses the voltage across R , connected between the

CL

dV = Change in voltage

dt = Change in time

CLP and DCIN pins. When this voltage exceeds 100mV,

the amplifier will override programmed charging current

to limit adapter current to 100mV/R . A lowpass filter

CL

The equivalent model of a set or parallel batteries is a

set of parallel capacitors. Since they are in parallel, the

change in voltage over change in time is the same for both

batteries 1 and ꢀ.

formed by 5kΩ and 0.1µF is required to eliminate switch-

ing noise. If the current limit is not used, CLP should be

connected to DCIN.

dV/dt

= dV/dt

BATꢀ

BAT1

100mV

CLP

+

From here we can simplify.

–

0.1µF

5kΩ

CL1

I

/C

= dV/dt = I

/C

BAT1 BAT1

BATꢀ BATꢀ

+

AC ADAPTER

INPUT

R

CL

*

= I

C /C

BAT1 BATꢀ BAT1

DCIN

BATꢀ

V

IN

+

At this point you can see that the current divides as the

ratio of the two batteries capacity ratings. The sum of the

currentintoboth batteries is the sameasthecurrent being

supply by the charger. This is independent of the mode of

the charger (CC or CV).

1760 F09

C

IN

100mV

ADAPTER CURRENT LIMIT

*R

=

CL

Figure 9.

Setting Input Current Limit

I

= I

+ I

BAT1 BATꢀ

CHRG

To set the input current limit, you need to know the mini-

mumwalladaptercurrentrating.Subtract52fortheinput

current limit tolerance and use that current to determine

the resistor value.

From here we solve for the actual current for each battery.

I

= I

C

/(C

+ C

)

BATꢀ

BAT1

CHRG BATꢀ BAT1

BATꢀ

C

/(C

CHRG BAT1 BAT1

R

I

= 100mV/I

LIM

CL

Please note that the actual observed current sharing will

vary from manufacturer’s claimed capacity ratings since

= Adapter Min Current

LIM

– (Adapter Min Current • 52)

1760fc

36

For more information www.linear.com/LTC1760

LTC1760

APPLICATIONS INFORMATION

As is often the case, the wall adapter will usually have at

least a +102 current limit margin and many times one

can simply set the adapter current limit value to the actual

adapter rating (see Figure 9 & Table 1).

Warning

DONOTCHANGETHEVALUEOFR

TION. The value must remain fixed and track the R_SENSE

value at all times. Changing the current setting can result

in currents that greatly exceed the requested value and

potentiallydamagethebatteryoroverloadthewalladapter

if no input current limiting is provided.

DURINGOPERA-

ILIMIT

Table 1. Common R_CLResistor Values

Adapter

Rating A

RCL Value*

(Ω) 1%

RCL Power

Dissipation (W)

RCL Power

Rating (W)

1.5

1.8

ꢀ

0.06

0.05

0.135

0.16ꢀ

0.18

0.ꢀ5

0.5

Setting Charger Output Voltage Limit

0.045

0.039

0.036

0.033

0.030

ThevalueofanexternalresistorconnectedfromtheV

LIMIT

ꢀ.3

ꢀ.5

ꢀ.7

3

0.ꢀ06

0.ꢀꢀ5

0.ꢀ41

0.ꢀ1

pin to GND determines one of five voltage limits that are

applied to the charger output value. See Table 3. These

limits provide a measure of safety with a hardware restric-

tion on charging voltage, which cannot be overridden by

software. This voltage sets the limit that will be applied

to the battery as reported by battery. Since the battery

internal voltage monitor point is the actual cell voltage,

you may see higher voltages, up to 51ꢀmV higher, at the

external charger terminals due to the voltage servo loop

action. See Operations “Section 3.7” for more information

on the voltage servo system.

0.5

*Values shown above are rounded to nearest standard value.

Table 1 RCL values take into account LTC1760 C-grade 52 tolerance for

VCL1.

Extending System to More than 2 Batteries

The LTC1760 can be extended to manage systems with

more than 3 sources of power. Contact Linear Technology

Applications Engineering for more information.

Table 3. Recommended Resistor Values for R_VLIMIT

Charge Termination Issues

V

R

VLIMIT

(Ω) 1%

MAX

Up to 8.4V

0 (Short to ground)

Batteries with constant-current charging and voltage-

based charger termination might experience problems

with reductions of charger current caused by adapter

limiting. It is recommended that input limiting feature be

defeated in such cases. Consult the battery manufacturer

for information on how your battery terminates charging.

Up to 1ꢀ.6V

10k

Up to 16.8V

33k

Up to ꢀ1.0V

100k

Up to 3ꢀ.7V (No Limit)

Open or short to V

CCꢀ

Inductor Selection

Setting Charger Output Current Limit

Higher operating frequencies allow the use of smaller

inductor and capacitor values. A higher frequency gener-

ally results in lower efficiency because of MOSFET gate

charge losses. In addition, the effect of inductor value

on ripple current and low current operation must also be

considered.Theinductorripplecurrent∆I decreaseswith

higher frequency and increases with higher V .

The LTC1760 current DAC and the PWM analog circuitry

must coordinate the setting of the charger current. Failure

to do so will result in incorrect charge currents.

Table 2. Recommended Resistor Values

L

I

(A)

R

SENSE

(Ω) 1%

R

(W)

R

(Ω) 1%

ILIMIT

MAX

SENSE

IN

1

0.100

0.ꢀ5

0.5

0

⎛

⎞

⎟

⎠

ꢀ

3

4

0.05

0.0ꢀ5

10k

33k

1

V_OUT

ΔI_L=

V_OUT1−

⎜

f L

( )( )

V

⎝

IN

0.5

Open or short to V

CCꢀ

Accepting larger values of ∆I allows the use of low

L

inductances, but results in higher output voltage ripple

1760fc

37

For more information www.linear.com/LTC1760

LTC1760

APPLICATIONS INFORMATION

and greater core losses. A reasonable starting point for

at high input voltage or during a short-circuit when

the duty cycle in this switch is nearly 1002. The term

(1 + d∆T) is generally given for a MOSFET in the form of a

setting ripple current is ∆I = 0.4(I

). In no case should

L

MAX

∆I exceed 0.6(I

) due to limits imposed by IREV and

L

MAX

CA1.Rememberthemaximum∆I occursatthemaximum

normalizedR

vsTemperaturecurve,butd=0.005/°C

L

DS(ON)

input voltage. In practice 10µH is the lowest value recom-

canbeusedasanapproximationforlowvoltageMOSFETs.

isusuallyspecifiedintheMOSFETcharacteristics.The

mended for use.

C

RSS

constant k = 1.7 can be used to estimate the contributions

of the two terms in the main switch dissipation equation.

Charger Switching Power MOSFET and Diode

Selection

If the LTC1760 charger is to operate in low dropout mode

or with a high duty cycle greater than 852, then the top-

side N-channel efficiency generally improves with a larger

MOSFET. Using asymmetrical MOSFETs may achieve cost

savings or efficiency gains.

TwoexternalpowerMOSFETsmustbeselectedforusewith

the LTC1760 charger: An N-channel MOSFET for the top

(main) switch and an N-channel MOSFET for the bottom

(synchronous) switch.

The peak-to-peak gate drive levels are set by the V volt-

The Schottky diode D1, shown in the Typical Application,

conducts during the dead-time between the conduction of

the two power MOSFETs. This prevents the body diode of

the bottom MOSFET from turning on and storing charge

during the dead-time, which could cost as much as 12

in efficiency. A 1A Schottky is generally a good size for

4A regulators due to the relatively small average current.

Larger diodes can result in additional transition losses

due to their larger junction capacitance. The diode may

be omitted if the efficiency loss can be tolerated.

CC

age.Thisvoltageistypically5.ꢀV.Consequently,logic-level

threshold MOSFETs must be used. Pay close attention to

the B

specification for the MOSFETs as well; many of

VDSS

the logic level MOSFETs are limited to 30V or less.

SelectioncriteriaforthepowerMOSFETsincludethe“ON”

resistance R

, reverse transfer capacitance C

DS(ON)

,

RSS

input voltage and maximum output current. The LTC1760

charger is always operating in continuous mode so the

duty cycles for the top and bottom MOSFETs are given by:

Main Switch Duty Cycle = V /V

Calculating IC Operating Current

OUT IN

Synchronous Switch Duty Cycle = (V – V )/V

This section shows how to use the values supplied in the

Electrical Characteristics table to estimate operating cur-

rent for a given application.

IN

OUT IN

The MOSFET power dissipations at maximum output

current are given by:

ꢀ

The total IC operating current through DCIN when AC is

P

= V /V (I

RSS

) (1 + d∆T)R

+ k(V )

MAIN

OUT IN MAX

DS(ON)

IN

present and batteries are charging (I

) is given by:

DCIN_CHG

(I

MAX

)(C )(f)

ꢀ

I

= I

+ I

+

DCIN_CHG

CH1

+I

VCCꢀ_AC1

+I

SAFETY1

SAFETYꢀ

+I

P

= (V – V )/V (I

) (1 + d∆T) R

SYNC

IN

OUT IN MAX

DS(ON)

+I

VLIM ILIM SMB SMB_BAT1 SMB_BATꢀ SMBALERT

Where d∆T is the temperature dependency of R

DS(ON)

where:

and k is a constant inversely related to the gate drive

ꢀ

current. Both MOSFETs have I R losses while the topside

I

is defined in “Electrical Characteristics.”

CH1

N-channel equation includes an additional term for transi-

tion losses, which are highest at high input voltages. For

is defined in “Electrical Characteristics.”

VCCꢀ_AC1

V < ꢀ0V the high current efficiency generally improves

isthecurrentusedtotestthebattery thermistor

SAFETYX

connected to SAFETY1 OR SAFETYꢀ.

IN

with larger MOSFETs, while for V > ꢀ0V the transition

IN

losses rapidly increase to the point that the use of a higher

For thermistors that are OVER-RANGE:

R

device with lower C

actually provides higher

DS(ON)

RSS

I

= ꢀ/64 • V

/(RXB + R

)

SAFETYX

VCCꢀ

THX

efficiency. The synchronous MOSFET losses are greatest

1760fc

38

For more information www.linear.com/LTC1760

LTC1760

APPLICATIONS INFORMATION

For thermistors that are COLD-RANGE:

I

= I

ILIM

+ I

SMB

+ I

SMB_BAT1

+ I

SMB_BATꢀ

+

SAFETYꢀ

DCIN_CHG

CH1

+ I

VCCꢀ_AC1

+ I

SAFETY1

+ I

I

= 4/64 • V

/(RXB + R

)

+ I

+

SAFETYX

VCCꢀ

THX

VLIM

SMBALERT

For thermistors that are IDEAL-RANGE:

= 4/64 • V /(RXB + R ) + ꢀ/64 • V /

VCCꢀ

= 1.3mA + 700µA + ꢀ18µA + ꢀ18µA +81µA + 81µA

+ 0µA + 5.4µA + 5.4µA + 0µA = ꢀ.6ꢀmA

I

SAFETYX

(R1A +R

VCCꢀ

THX

)

THX

The total operating current through BAT1 and BATꢀ when

AC is not present (I

For thermistors that are HOT-RANGE:

= 4/64 • V /(RXB + R ) + 4/64 • V /

VCCꢀ

) is given by:

BAT_NOAC

I

SAFETYX

(R1A +R

VCCꢀ

THX

)

I

= I + I

SMB_BAT1_AC0

+ I

+

THX

BAT_NOAC

SMB

BAT

VCCꢀ_AC0

SAFETY1

SAFETYꢀ

+ I

SMB_BATꢀ_AC0 SMBALERT

R

is the impedance of the battery’s thermistor to

THX

ground.

where:

RXB = 54.9k

I

is defined in “Electrical Characteristics.”

BAT

RXA = 1.13k

is defined in “Electrical Characteristics.”

VCCꢀ_AC0

Sample calculation of I

with V

= 5.ꢀV

is the current used to test the battery

SAFETYX

thermistor connected to SAFETY1 or SAFETYꢀ.

SAFETYX

VCCꢀ

Thermistor Impedance

R

(W)

Thermistor Range

OVER_RANGE

I

(µA)

THX

SAFETYX

I

= ꢀ/64 • V /(RXB + R ).

SAFETYX

VCCꢀ

THX

400

1.05

R

is the impedance of the battery’s thermistor to

THX

3.3k

400

IDEAL_RANGE

UNDER_RANGE

4ꢀ.ꢀ

ꢀ18

ground.

RXB = 54.9k.

I

= V

/(R

+ R

).

VLIMIT

VCCꢀ

VLIMIT

LIM_PU

Sample calculation of I

with V

= 5.ꢀV

SAFETY

VCCꢀ

= V

/(R

+ R

).

ILIMIT

VCCꢀ

ILIMIT

LIM_PU

Thermistor Impedance

R

is the typical pull-up impedance at V

LIMIT

LIMIT.

LIM_PU

and I

R

(Ω)

Thermistor Range

I

(µA)

SAFETYX

THX

400

UNDER_RANGE

ꢀ.9

R

= 34k.

LIM_PU

I

is the current used for communicat-

SMB_BATX_ACO

ing with Battery1 or Batteryꢀ when AC in not present.

R

is the value of the resistance from V

to

VLIMIT

GND.

LIMIT

I

= 350µA • 0.00687 = ꢀ.404µA.

SMB_BATX_AC0

R

is the value of the resistance from I

to

ILIMIT

GND.

LIMIT

is the current used for communicating with the

SMB

SMBus Host and depends on the amount of bus

traffic.

I

is the current used for communicating with the

SMB

SMBus Host and depends on the amount of bus traffic.

Sample calculation with two Li-Ion batteries (R

400), V

=

THX

= 5.ꢀV, and no SMBus Host communication:

I

is the current used for communicating

CCꢀ

SMB_BATX

with Battery1 or Batteryꢀ.

I

– I + I

SMB_BAT1_AC0

+ I

SMBALERT

+

SAFETYꢀ

BAT_NOAC

SMB

BAT

VCCꢀ_AC0

SAFETY1

+ I

I

= 350µA • 0.0155 = 5.4ꢀ5µA.

SMB_BATꢀ_AC0

SMB_BATX

SMBALERT

= 175µA + 80µA + ꢀ.9µA + ꢀ.9µA + 0µA + ꢀ.4µA +

is defined in “Electrical Characteristics.”

ꢀ.4µA + 0µA = ꢀ65µA

Sample calculation of I

with two Li-Ion batteries

DCIN_CHG

(R

= 400), R

= R

= 30k, V

= 5.ꢀV, and

CCꢀ

THX

VLIMIT

ILIMIT

no SMBus Host communication:

1760fc

39

For more information www.linear.com/LTC1760

LTC1760

APPLICATIONS INFORMATION

Calculating IC Power Dissipation

Capacitors C and C are used to filter the V delta-

DAC

B1

Bꢀ

sigma modulation frequency components to a level which

The power dissipation of the LTC1760 is dependent

is essentially DC. C is the primary filter capacitor and

Bꢀ

upon the gate charge of Q and Q .(Refer to Typical

TG

BG

CB1 is used to provide a zero in the response to cancel

Application). The gate charge is determined from the

manufacturer’sdatasheetandisdependentuponboththe

gate voltage swing and the drain voltage swing of the FET.

the pole associated with C . Acceptable voltage ripple

Bꢀ

at V

is about 10mV . Since the period of the delta-

SET

P-P

∆S

sigma switch closure, T , is about 11µs and the internal

P = (V

DCIN_CHG

– V ) • f

• (Q + Q ) + V

•

V

DAC

resistor, R

, is 7.ꢀkΩ, the ripple voltage can be

D

DCIN

VCC

• (I

OSC

TG

+ I

BG

)

DCIN

VSET

I

– V

approximated by:

V_REF• T_Δ∑

R_VSETC ||C

Bꢀ

VCC

SAFETY1

SAFETYꢀ

where:

ΔV_VSET

=

(

)

I

, I

are defined in the

B1

DCIN_CHG SAFETY1 SAFETYꢀ

previous section.

Example:

= 5.ꢀV, V

Then the equation to extract C || C is:

B1

Bꢀ

V_REF• T_Δ∑

C_B1||C_Bꢀ=

V

= 19V, f

= 345kHz, Q

=

VCC

DCIN

OSC

= ꢀ.6ꢀmA, I

TG

R

_VSETΔV_VSET

Q

= 15nC, I

=

BG

SAFETYꢀ

P = 190mW

D

DCIN_CHG

= ꢀ18µA.

SAFETY1

I

C

should be 10× to ꢀ0× C to divide the ripple voltage

B1

Bꢀ

present at the charger output. Therefore C = 0.01µF and

B1

C

= 0.1µF are good starting values. In order to prevent

Bꢀ

V /I Capacitors

SET SET

overshoot during start-up transients the time constant as-

sociated with C must be shorter than the time constant

Capacitor C7 is used to filter the delta-sigma modulation

frequency components to a level which is essentially DC.

Acceptable voltage ripple at I is about 10mV . Since

the period of the delta-sigma switch closure, T , is about

10µs and the internal I

ripple voltage can be approximated by:

Bꢀ

of C5 at the I pin. If C is increased to improve ripple

TH

Bꢀ

rejection, then C5 should be increased proportionally and

charger response time to voltage variation will degrade.

SET

P-P

∆S

resistor, R , is 18.77k, the

DAC

SET

Input and Output Capacitors

In the 4A Lithium Battery Charger (Typical Application

V_REF• T_Δ∑

R_SET•C7

section), theinputcapacitor(C )isassumedtoabsorball

ΔV

=

IN

ISET

input switching ripple current in the converter, so it must

haveadequateripplecurrentrating.Worst-caseRMSripple

currentwillbeequaltoonehalfofoutputchargingcurrent.

Actual capacitance value is not critical. Solid tantalum

low ESR capacitors have high ripple current rating in a

relatively small surface mount package, but caution must

be used when tantalum capacitors are used for input or

output bypass. High input surge currents can be created

when the adapter is hot-plugged to the charger or when a

battery is connected to the charger. Solid tantalum capaci-

tors have a known failure mechanism when subjected to

very high turn-on surge currents. Only Kemet T495 series

of “Surge Robust” low ESR tantalums are rated for high

surge conditions such as battery to ground.

Then the equation to extract C7 is:

V_REF• T_Δ∑

C7 =

ΔV

•R_SET

ISET

= 0.8/0.01/18.77k(10µs) @ 0.043µF

In order to prevent overshoot during start-up transients

the time constant associated with C7 must be shorter than

the time constant of C5 at the I pin. If C7 is increased

to improve ripple rejection, then C5 should be increased

proportionally and charger response time to average cur-

rent variation will degrade.

TH

1760fc

40

For more information www.linear.com/LTC1760

LTC1760

APPLICATIONS INFORMATION

The relatively high ESR of an aluminum electrolytic for

C15, located at the AC adapter input terminal, is helpful

in reducing ringing during the hot-plug event. Refer to

AN88 for more information.

current. FortheN-channelchargepath, themaximumcur-

rent is the maximum programmed current to be used. For

the P-channel discharge path maximum current typically

occurs at end of life of the battery when using only one

battery. The upper limit of R

value is a function of

DS(ON)

Highest possible voltage rating on the capacitor will

minimize problems. Consult with the manufacturer before

use. Alternatives include new high capacity ceramic (at

least ꢀ0µF) from Tokin, United Chemi-Con/Marcon, et al.

Other alternative capacitors include OSCON capacitors

from Sanyo.

the actual power dissipation capability of a given MOSFET

package that must take into account the PCB layout. As a

starting point, without knowing what the PCB dissipation

capability would be, derate the package power rating by

a factor of two.

P_MOSFET

R_DS(ON)MAX

=

The output capacitor (C ) is also assumed to absorb

OUT

ꢀ

ꢀ I

(

)

MAX

output switching current ripple. The general formula for

capacitor current is:

If you are using a dual MOSFET package with both MOS-

FETs in series, you must cut the package power rating in

half again and recalculate.

V

BAT

0.29 (V ) 1 –

BAT

(

)

V

DCIN

I

=

P_MOSFETDUAL

RMS

(L1)(f)

R_DS(ON)MAX

=

ꢀ

4 I

(

)

MAX

For example:

If you use identical MOSFETs for both battery paths,

voltage drops will track over a wide current range. The

LTC1760 linear ꢀ5mV CV drop regulation will not occur

until the current has dropped below:

V

= 19V, V = 1ꢀ.6V, L1 = 10µH, and

BAT

DCIN

f = 300kHz, I

= 0.41A.

RMS

EMI considerations usually make it desirable to minimize

ripple current in the battery leads, and beads or inductors

maybeaddedtoincreasebatteryimpedanceatthe300kHz

switching frequency. Switching ripple current splits be-

tween the battery and the output capacitor depending on

theESRoftheoutputcapacitorandthebatteryimpedance.

If the ESR of C

raised to 4Ω with a bead or inductor, only 52 of the cur-

rent ripple will flow in the battery.

ꢀ5mV

I_LINEARMAX

=

ꢀR_DS(ON)MAX

However, if you try to use the above equation to determine

R

to force linear mode at full current, the MOSFET

value becomes unreasonably low for MOSFETs

DS(ON)

is 0.ꢀΩ and the battery impedance is

OUT

available at this time. The need for the LTC1760 voltage

drop regulation only comes into play for parallel battery

configurations that terminate charge or discharge using

voltage. At first this seems to be a problem, but there are

several factors helping out:

PowerPath and Charge MUX MOSFET Selection

Three pairs of P-channel MOSFETs must be used with

the wall adapter and the two battery discharge paths. Two

pairsofN-channelMOSFETsmustbeusedwiththebattery

charge path. The nominal gate drive levels are set by the

clamp drive voltage of their respective control circuitry.

This voltage is typically 6.ꢀ5V. Consequently, logic-level

threshold MOSFETs must be used. Pay close attention to

1. When batteries are in parallel current sharing, the cur-

rent flow through any one battery is less than if it is

running stand-alone.

ꢀ. Most batteries that charge in constant voltage mode,

such as Li-ion, charge terminate at a current value of

C/10 or less which is well within the linear operation

range of the MOSFETs.

the B

specification for the MOSFETs as well; many of

VDSS

the logic level MOSFETs are limited to 30V or less.

3. Voltage tracking for the discharge process does not

need such precise voltage tracking values.

SelectioncriteriaforthepowerMOSFETsincludethe“ON”

resistance R

, input voltage and maximum output

DS(ON)

1760fc

41

For more information www.linear.com/LTC1760

LTC1760

APPLICATIONS INFORMATION

The LTC1760 has two transient conditions that force the

dischargepathP-channelMOSFETstohavetwoadditional

parameters to consider. The parameters are gate charge

Remember to only use the real wall adapter with a produc-

tionDCpowercordwhenperformingthewalladapterpath

test. The use of a laboratory power supply is unrealistic

for this test and will force you to over specify the MOSFET

ratings.Abatterypackusuallyhasenoughseriesresistance

to limit the peak current or are too low in voltage to create

enough instantaneous power to damage their respective

power path MOSFETs.

Q

GATE

and single pulse power capability.

When the LTC1760 senses a LOW_POWER event, all

the P-channel MOSFETs are turned on simultaneously

to allow voltage recovery due to a loss of a given power

source. However, there is a delay in the time it takes to

turn on all the MOSFETs. Slow MOSFETs will require more

bulk capacitance to hold up all the system’s power sup-

ply function during the transition and fast MOSFET will

require less bulk capacitance. The transition speed of a

MOSFET to an on or off state is a direct function of the

MOSFET gate charge.

Conditioning Systems With Large Loads

In systems where the load is too large to be used for

conditioning a single battery it may be necessary to

bypass the built in calibrate function and simply switch

in an external load. A convenient way to accomplish this

task is by using an SMBus based LTC16ꢀ3 load switch

controller. See Figure 10.

t = Q

/I

GATE DRIVE

I

is the fixed drive current into the gate from the

DRIVE

LTC1760 and “t” is the time it takes to move that charge

to a new state and change the MOSFET conduction mode.

TO

LOAD

PowerPath

MUX

HencetimeisdirectlyrelatedtoQ

.SinceQ

goesup

LTC1760

GATE

with MOSFETs of lower R

, choosing such MOSFETs

CHARGE

MUX

DS(ON)

has a counterproductive increase in gate charge making

theMOSFETslower.PleasenotethattheLTC1760recovery

time specification only refers to the time it takes for the

voltagetorecovertotheleveljustpriortotheLOW_POWER

event as opposed to full voltage.

SMBus

The single pulse current rating of MOSFET is important

when a short-circuit takes place. The MOSFET must

SMBus

TO/FROM

HOST

CONDITIONING

LOAD

LTC1623

survive a 15ms overload. MOSFETs of lower R

DS(ON)

or MOSFETs that use more powerful thermal packages

will have a high power surge rating. Using too small of a

pulse rating will allow the MOSFET to blow to the open

circuit condition instantly like a fuse. Typically there is no

outward sign of failure because it happens so fast. Please

measure the surge current for all discharge power paths

under worse case conditions and consult the MOSFET

data sheet for the limitations. Voltage sources with the

highest voltage and the most bulk capacitance are often

the biggest risk. Specifically the MOSFETs in the wall

adapter path with wall adapters of high voltage, large

bulk capacitance and low resistance DC cables between

the adapter and device are the most common failures.

1760 F10

Figure 10. Large Load Conditioning Circuit

Unique Configuration Information

This section summarizes unique LTC1760 configurations

thatallowsome LTC1760featurestobeeliminated. These

configurations may be selected in any combination with-

out adversely affecting LTC1760 operation. Refer to the

Typical Application circuit diagram located at the back of

this data sheet.

1760fc

42

For more information www.linear.com/LTC1760

LTC1760

APPLICATIONS INFORMATION

A) Single Battery Configuration.

5) RemoveallcomponentsconnectedtoCOMP1,V

,

SET

I , I , I

and V

pins.

TH SET LIMIT

LIMIT

To limit the LTC1760 to a single battery, modify the

battery slot to be eliminated as follows:

6) Short I

and V

to GND.

LIMIT

1) Remove both FETs (Q5, Q6 or Q7, Q8) involved in

the discharge path.

7) Remove R1, C1 but short CLP to DCIN. Replace

with a short/trace connection.

R

CL

ꢀ) Remove both FETS (Q3, Q4 or Q9, Q10) involved in

the charge path.

8) ShortCSPtoCSNbutleavethecombinationfloating.

9) Unless otherwise specified, leave the unused pins

of the LTC1760 floating.

3) Removethethermistorsensingresistors(R1A, R1B

or RꢀA, RꢀB).

F) No DC Path And No Charge Configuration.

4) Short the thermistor sense lines (TH1A, TH1B or

THꢀA, THꢀB) together at the IC.

To limit the LTC1760 to battery discharge functions

only, merge the previous two configurations with the

following:

5) Remove the diode (Dꢀ or D3).

6) Unless otherwise specified, leave the unused pins

of the LTC1760 floating.

1) Remove C .

IN

ꢀ) Remove resistors tied to DCDIV. Ground DCDIV.

B) No Short-Circuit Protection Configuration.

PCB Layout Considerations

1) Replace R with a short.

SC

Formaximumefficiency,theswitchnoderiseandfalltimes

should be minimized. To prevent magnetic and electrical

field radiation and high frequency resonant problems,

proper layout of the components connected to the IC is

essential. (See Figure 11.) Here is a PCB layout priority list

for proper layout. Layout the PCB using this specific order.

C) No LOPWR Protection.

1) Remove resistors Rꢀ and R3 connected to LOPWR

and tie LOPWR to the V pin.

CC

D)No DC Path Configuration.

ToremovetheDCinputaspartofthepowerpathchoices

to support the load:

1. Input capacitors need to be placed as close as possible

to switching FET’s supply and ground connections.

Shortest copper trace connections possible. These

parts must be on the same layer of copper. Vias must

not be used to make this connection.

1) Remove both FETs Q1 and Qꢀ involved in the DC

path.

ꢀ) Unless otherwise specified, leave the unused pins

of the LTC1760 floating.

E) No Charge Configuration.

SWITCH NODE

L1

V

BAT

To permanently disable the battery charger function:

1) Remove ALL FETs involved in the charge path (Q3,

Q4, Q9, Q10).

HIGH

FREQUENCY

CIRCULATING

PATH

C

IN

D1

C

OUT

V

IN

BAT

ꢀ) Remove switching FETs QTG, QBG, diode D1 and

inductor L1.

1760 F10

3) RemovediodesDꢀ, D3, D4, capacitorsC4, C

and

OUT

Resistor R11 and R

.

Figure 11. High-Speed Switching Path

SENSE

4) Reduce C capacitor to 0.1µF.

IN

1760fc

43

For more information www.linear.com/LTC1760

LTC1760

APPLICATIONS INFORMATION

ꢀ. The control IC needs to be close to the switching FET’s

gate terminals. Keep the gate drive signals short for a

cleanFETdrive.ThisincludesICsupplypinsthatconnect

to the switching FET source pins. The IC can be placed

on the opposite side of the PCB relative to above.

9. A good rule of thumb for via count for a given high

current path is to use 0.5A per via. Be consistent.

10. If possible, place all the parts listed above on the

same PCB layer.

11.Copperfillsorpoursaregoodforallpowerconnections

3. Place inductor input as close as possible to switching

FET’s output connection. Minimize the surface area of

this trace. Make the trace width the minimum amount

needed to support current—no copper fills or pours.

Avoid running the connection using multiple layers in

parallel. Minimize capacitance from this node to any

other trace or plane.

-

except as noted above in Rule 3. You can also use cop

per planes on multiple layers in parallel too—this helps

with thermal management and lower trace inductance

improving EMI performance further.

1ꢀ. For best current programming accuracy provide a

Kelvin connection from R

Figure 1ꢀ as an example.

to CSP and BAT. See

SENSE

4. Place the output current sense resistor right next to

the inductor output but oriented such that the IC’s

current sense feedback traces going to resistor are not

long. The feedback traces need to be routed together

as a single pair on the same layer at any given time

with smallest trace spacing possible. Locate any filter

component on these traces next to the IC and not at

the sense resistor location.

It is important to keep the parasitic capacitance on the R ,

T

CSP and BAT pins to a minimum. The traces connecting

these pins to their respective resistors should be as short

as possible.

DIRECTION OF CHARGING CURRENT

R

SNS

5.Placeoutputcapacitorsnexttothesenseresistoroutput

and ground.

1760 F11

6. Output capacitor ground connections need to feed into

samecopperthatconnectstotheinputcapacitorground

before tying back into system ground.

CSN

CSP

Figure 12. Kelvin Sensing of Charging Current

General Rules

Important Safety Notes

7. Connection of switching ground to system ground or

internal ground plane should be single point. If the

system has an internal system ground plane, a good

way to do this is to cluster vias into a single star point

to make the connection.

Although every effort is made to meet and exceed all

required “SMBus Charger V1.1” safety features it is the

responsibility of the battery pack to protect itself from

excessive currents or voltages. The LTC1760 is not itself

a safety device. Consult your battery pack manufacturer

for more information.

8. Route analog ground as a trace tied back to IC ground

(analog ground pin if present) before connecting to any

other ground. Avoid using the system ground plane.

CAD trick: make analog ground a separate ground net

and use a 0Ω resistor to tie analog ground to system

ground.

1760fc

44

For more information www.linear.com/LTC1760

LTC1760

TYPICAL APPLICATIONS

PowerPath MUX

R

CL

0.03Ω

V

IN

R10

100Ω

C8

1µF

C9

C1

0.1µF

Q1

Q6

Q5

Q7

Q8

R1

4.99k

0.1µF

LTC1760

Q2

36

41

3

1

7

6

9

V

CLP

DC

BAT1

BAT2

PLUS

GDCI

GDCO

GB1I

GB1O

GB2I

GB2O

SCP

SCN

IN

R4

100pF

2

12.7k

8

11

10

5

R

SC

0.02Ω

R5

1.21k

16

37

47

48

46

45

13

40

24

4

DCDIV

COMP1

GCH2

SCH2

GCH1

SCH1

LOAD

12

34

35

14

15

42

43

44

39

38

28

27

17

21

30

31

19

23

LOPWR

CSN

CSP

R2

280k

R7

49.9k

CL

20µF

C11

1800pF

I

TH

R3

49.9k

C3

I

SET

R9

0.012µF

SW

BOOST

TGATE

BGATE

PGND

TH2A

TH2B

SCL2

SDA2

TH1A

TH1B

SCL1

V

3.3k

C12

100pF

SET

C7

0.1µF

V

CC

GND

V

DDS

C5

0.15µF

SMBALERT

SCL

V

*

DDS

R2A, 1.13k

25

29

18

22

20

33

32

26

BAT2

R

PU

R

PU

V

CC2

R2B, 54.9k

TH

SMBALERT

SCL

SCL2

SDA2

SDA

SCL

SDA

V

DDS

V

DDS

R1A, 1.13k

R1B, 54.9k

V

I

LIMIT

MODE

R

VLIMIT

10k

SDA1

C1

0.1µF

V

*

DDS

BAT1

TH

SCL

SDA

SCL1

SDA1

BAT2

D2

BAT1

D3

QTG

QBG

C

IN

20µF

C4

0.22µF

R11

1k

L1

10µH

D4

C

OUT

20µF

R

SENSE

0.025

C6

4.7µF

C13

0.1µF

D1

CB2

0.47µF

CB1

0.1µF

CHARGE

MUX

R6

100Ω

Q4

Q3

Q9

Q10

BAT1

BAT2

1760 TA02

D1: MBR130T3

D2, D3: BAT54A TYPE

D4: CMDSH3 TYPE

Q1, Q2, Q5, Q6, Q7, Q8: Si4925DY

Q3, Q4, Q9, Q10, QTG, QBG: FDS6912A

*OPTIONAL: ESD CLAMP DIODES FOR BATTERY HOT SWAP PROTECTION

1760fc

45

For more information www.linear.com/LTC1760

LTC1760

PACKAGE DESCRIPTION

Please refer to http://www.linear.com/product/LTC1760#packaging for the most recent package drawings.

FW Package

48-Lead Plastic TSSOP (6.1mm)

(Reference LTC DWG # 05-08-1651 Rev A)

12.40 – 12.60*

(.488 – .496)

48

25

0.95 0.10

6.2 0.10

44

42

41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25

48 47 46 45

43

8.4 0.10

7.9 – 8.3

(.311 – .327)

1

24

0.32 0.05

0.50 BSC

5

7

8

1

2

3

4

6

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

RECOMMENDED SOLDER PAD LAYOUT

1.10

(.0433)

MAX

6.0 – 6.2**

(.236 – .244)

0.25

REF

0° – 8°

-T-

-C-

0.10 C

FW48 TSSOP REV A 1005

0.50

(.0197)

BSC

0.17 – 0.27

(.0067 – .0106)

TYP

0.09 – 0.20

(.0035 – .008)

0.45 – 0.75

(.018 – .029)

0.05 – 0.15

(.002 – .006)

NOTE:

1. CONTROLLING DIMENSION: MILLIMETERS

MILLIMETERS

2. DIMENSIONS ARE IN

(INCHES)

3. DRAWING NOT TO SCALE

*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDE

**

DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE

1760fc

46

For more information www.linear.com/LTC1760

LTC1760

REVISION HISTORY

REV

DATE

DESCRIPTION

PAGE NUMBER

A

04/11 I-Grade part added. Reflected throughout the data sheet

1-48

3

B

03/16 Revised Conditions of V Load Regulation Spec

CC

C

08/17 Revised Circuit Diagram C5 & C7, BAT1, BATꢀ added

45

1760fc

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

47

For more information www.linear.com/LTC1760

LTC1760

RELATED PARTS

PART NUMBER

LT^®1571

DESCRIPTION

COMMENTS

1.5A Switching Regulator Battery Charger

Li-Ion Linear Charger with Thermal Regulation

ꢀA Switching Regulator Battery Charger

Dual Battery Charger/Selector with SPI

500kHz or ꢀ00kHz Switching Frequency for Small Design

Will Not Overheat, Standalone Charger, Complete Charger

Monolithic, ꢀ0-Lead TSSOP, ꢀ8-Lead SSOP Packages

LTC1733

LT1769

LTC1960

LTC4006

11-Bit V , 0.82 Voltage Accuracy, 10-Bit I

for 52 Current Accuracy

DAC

Small, High Efficiency, Fixed Voltage,

Lithium-Ion Battery Charger

Constant Current/ Constant Voltage Switching Regulator

with Termination Timer; AC Adapter Current Limit and

SafetySignal Sensor in a Small 16 Pin Package

LTC4007

LTC4008

High Efficiency, Programmable Voltage

Battery Charger with Termination

Complete Charger for 3- or 4-Cell Lithium-Ion Batteries,

AC Adapter Current Limit, SafetySignal Sensor and Indicator Outputs

High Efficiency, Programmable Voltage/

Current Battery Charger

Constant Current/ Constant Voltage Switching Regulator;

Resistor Voltage/Current Programming, AC Adapter Current

Limit and SafetySignal Sensor

LTC4100

Smart Battery Charger Controller

SMBus Rev 1.1 Compliant

1760fc

LT 0817 REV C • PRINTED IN USA

www.linear.com/LTC1760

48

 LINEAR TECHNOLOGY CORPORATION 2010

For more information www.linear.com/LTC1760


型号：	LTC1760CFW#PBF
厂家：	Linear
描述：	LTC1760 - Dual Smart Battery System Manager; Package: TSSOP; Pins: 48; Temperature Range: 0°C to 70°C 电池光电二极管
文件：	总48页 (文件大小：396K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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